The Fram OCOD issues were really overblown back when they were having issues with them, and the whole 'cardboard' endcaps thing is also been distorted by internet rumor. I would not fear the OCOD anymore, but for the same $$ there are better filters. The Fram Ultra is very well designed and made with very high efficiency wire backed media, I think it is 99% efficient at 20 microns and 80% efficient at 10 microns. For the 9$ price tag they cannot be beat, in my opinion.
The Purolators went downhill towards the end of the white can days, with uneven pleat spacing by the seam leading to tearing of the media nearer the baseplates. Motorcraft FL1a is/was made by purolator. Purolator has changed ownership lately and who makes what for whom is not something I really keep upto date on. I did like the thread end bypass on the FL-1a and when I opened up the one I used, it showed no evidence of tearing at the seam.
Regardig your 60psi oil pressure at highway speeds, I forgot you have a 3 speed 727, which likely runs close to 3K rpm at 65mph with 3.55:1 rear gears. Mine runs ~1975rpm at 65mph with Overdrive and lockup and 3:55's as I have the more delicate A500 or 42rh trasmission. Next time I am at 65mph an hot I will take it out of OD and see what PSI mine goes to in third, but in OD at 1975 rpm mine sits at 42 PSI as hot as it gets, and this number is also checked a bit more often as my OEM temp gauge has been reading higher than normal lately, but the Oil pressure gauge has not fluctuated from 42 PSI at 65mph, and if it were indeed running hotter the oil should be thinner and thus have less PSI.
The dashboard voltage limiter(5 volts) on mine started acting a bit funny and rather than spend 35+$ for a new one, I used a 8$ modern solid state voltage bucker to send 5v to the gauges, but I have not verified lately that this 5.00v I set it has not drifted in the last few years. Before going with this new voltage limiter the temp gauge on hot restart would shoot upto the H before settling midway, with the newer limiter it will only slowly rise after a hot restart.
Since I have not trusted my OEM coolant temp gauge for a while, and the Oil PSI is only somewhat reassuring that I am not running hotter than desirable, I have used thermal epoxy to adhere a K type thermocouple to my thermostat housing, and a few other areas, like my alternator. The k type is the same as provided with many digital multimeters, and I have a device which can display the readings of 4 Ktype thermocouples at once. The one on my T stat housing reads 180f +/- 2*f at highway speed, but when I slow to a red light at an offramp, it will quickly climp to 196f, but then just as quickly lower back to 194.5 and stay there, indicating the thermostat has opened enough to keep the intended 195f. This is reassuring as my OEM temp gauge might read normal or almost a full hatch mark above normal. I want to cover this area to protect it from windflow so as to get more accurate readings at highway speeds.
Seems modern manufactures thermostats, whether Stant superstats or Motorrad or Gates are all quite Junky. Mine seem slow to open fully on initial warm up, looking at the OEM gauge.
Obviously the airflow over the engine is responsible for the 180f reading at highway speeds and once stopped the flow from the fan is not enough to really reduce the temp reading and it more or less indicates true engine temperature.
Anyway i would certainly be much less comfortable ignoring the OEM gauge without the Oil PSI and the K type thermocouple on the t stat housing which indicate all is well, that the OEM temp gauge is not to be trusted.
I installed the Ktype on the T stat housing August of 2017 as it was reading high, but after a longer road trip it started reading normally again, until my recent cross country journey last November, when in Texas when it started reading high and I plugged in my 4 k type teperature gauge to see all was still well and as expected, which it was, which allowed me not to freak out about the higher than normal OEM gauge reading.
I cannot explain the inconsistent unexpected swings of the oem temp gauge, but Oh well.
As far as changing out the oil more frequently than 3K miles, the only way I would do that is if it was over a year since the last oil change, or the Oil smelled like gas from running too rich, or the Oil PSI read much lower than expected indicating the oil sheared to a lighter weight or perhaps an internal engine issue.
When one changes the oil, the fresh new detergents can strip off the ZDDP layers and other extreme pressure/antiwear additives that the previous oil has laid down over time with heat and pressure. If the engine is run hard right after an oil change, the new oil might possibly have stripped off these protective layers, and not yet had time to place its own down on the bearings/cam lobes, thus increasing engine wear.
So unless you know the oil is sheared or contaminated, or simply too old, changing it more frequently is NOT doing the engine any favors and could increase engine wear. Conventional oils of today( versus even 15 years ago) can easily go 5K miles and Synthetics 7500, but gasoline direct injected modern engines are having fuel dilution issues and manufacturers are recommending shorter oil change intervals that what the owners manuals originally stated.
I think I am about 5.5k Miles on this oil change since October 2018, and do not intend to change the Pennzoil Platinum sn+ 10w-30 until I am back in California, no less than 2600+ miles from now. In the ~5.5k miles I have driven this OCI. I have added 1 quart make up oil. Since wally world's 5qt jugs are inexpensve, I have been using Mobil 1 for the last 10+ years, and even though I never have cold start requirements, I was using Mobil1 0w-40 as it is such a good oil, the basestocks required to meet the 0w-xx specs needing to be a higher percentage of PAO ( group4) and esters( group5), rather than just Hydrocracked mineroils( group3). M1 0w-40 when I first used it made my engine much quieter over the previous M1 10w-40HM oil or the TDT 5w-40 I had been using previously, which in turn were quieter than the valvoline or castrol 10w-40s previous th that. Synthetics pretty much totally eliminated the lifter ticking on startup, warm or cold, which was enough for me to stay with Synthetics.
My latest Oil change Wal mart was out of M1 0w-40, and I was pretty much had decided to try something different anyway. On special I decided to go with eh pennzoil platinum SN+ 10w-30 @22.97 for a 5 quart jug and on startup a one particular annoying valvetrain type noise, that has been present for 50K miles diminished by 75% within 10 seconds of idling. And this quieter factor has remained at 5500+ miles later into the oil change. So needless to say I was surprised and very pleased, and will be sticking with This Oil for the forseeable future.
While it is hard to believe different oils can change the engine noise so significantly, the fact is that they do. Whether this noise equates to less engine wear cannot be determined without teardown style testing with all variables removed, but less noise is comforting. The PP 10w-30 is also showing slightly higher hot idle rpm (20) oil PSi than the M1 0w-40 did (18PSI) towards the end of the oil change interval , but slightly lower 2K rpm hot PSI. I do not really understand how that is functioning, unless the M1 is absorbing more engine heat at lower rpms. M1 0w-40 does use thinner basestocks than PP10w-30 which uses a gas to liquid basestock, but it has a higher 100C viscosity as well as HTHS viscosity due to the different types and amounts of viscosity index improvers.
The PP oil did go darker quicker but this can be expected when an oil known for high detergency is used in place of a different oil, and oil color is not really indicative of oil condition. Non detergent motor oils likely change color very little as the contaminants are sticking tothe insides of the engine rather than held in suspension by the motor oil.
Anyway QS 10w-30 is a known good oil. I'd not worry so much about original specs. My owners manual specifically says NOT to use 10w-40, because 10w-40s of that era were known to quickly shear/degrade into a sub 20 weight oil and not provide sufficient film strength to keep metal from touching metal. So that owners manual recommendation was relevant in 1989 but totally irrelevant with today's better viscosity index improvers/base stocks, and motor oils in general. Whether a 40w is required is debateable fo course, it could just lead to more drag from pumping losses and provide NO additional benefit, unless the engine were to overheat or run at elevated temperatures on the track, or the engine was prone to issues that are known to be resolved or mitigated with thicker oil, like piston slap which some newer GM engines are known for.
What is Good about 40 weight oils is they do NOT have to comply with lower ZDDP requirements of Xw-20 and Xw-30 weight oils, and ZDDP is good for flat tappet cams. Higher ZDDp on an oil burner can contaminate catalytic converters so they restrict the amount in SN rated oils, but not in the 40 weights or thicker. I forget the exact numbers but I think they are limited to no more than 900PPM of zinc or phosphorus, where about 1200 is said to be the ideal range for an oil with flat tappet cam lifters.
If you are looking for higher ZDDP oils then the diesel rated oils like shell Rotella have it, and are both diesel and gasoline rated and come in 10w-30 and 15w-40 and 20w-50.
Since ZDDp has been limited in 20 and 30 weight oils in the SN rating they have moved onto other additives, like Moly amd Boron and even titanium to replace the ZDDP as an antiwear/extreme pressure additive, but ZDDp is also an Antioxidant and many say that these newer AW and EP additives cannot replace it, especially in flat tappett cams.
As to whether your 1988 LA 360 has a roller cam, this Allpar site seems to indicate the 360 did not get the roller cam until 1989 while the 318 got the roller cam starting in 85, in trucks/vans. I could be reading it wrong though.https://www.allpar.com/mopar/318.html
Anyway I am no tribologist, but I am not an 'Oil is Oil' type of guy. There are significant differences between brands formuations and weights, Whether these differences will make any difference in engine longevity is highly debateable. For me I want a Quiet oil, that is not going to easily shear to too thin a viscosity, keep my engine internals free of varnish and sludge, and can fight acidity for at least 10K miles in 6 months, or 2K miles in 14 months.
I did have a few sub 20f Starts at high altitude with PP 10w-30SN+ oil on my cross country journey and the engine had Zero Issues starting. It did stall when i put it into reverse though even with symthetic ATF+4.
Another thing about Synthetic oils, since they are likely to clean better, they can strip the gunk which was preventing oil from leaking past old gaskets and seals. So while Synthetics might 'reveal' oil leaks, they will not cause oil leaks, but the result is the same, and High mileage Synthetic oils might be enough to prevent revealing these leaks.
Really interms of wear, Modern Synthetics do no better than modern conventional/mineral oils, what they can do is last much longer before requiring to be changed and have much better cold flow characteristics for those who might be starting their engines in sub 0f.
I have NO fear of pushng the PP 10w-30 7500+ miles of mostly highway driving, which will allow me to change it once I return to California in a month or so, but if I were using conventional I would be stressed at pushing it that long, and likely be changing it before the trip. Doing so in my parents driveways is technically not allowed by the HOA, so I'd really have to go somewhere else to do it, or Pay someone else to do it, and I trust no Iffy lube joint to not strip my oil pan, or use a good oil of the proper viscosity and use a good filter as well. So The somewhat higher priced Synthetic is not only peace of mind, but also saving me money in the long run and running quieter too.