I am going to try and detail as much as I can. If I can't get specific part numbers, I will try to get correct measurements, BUT YOU SHOULD CONFIRM MEASUREMENTS BEFORE INSTALLING.
It is very straight forward, but I am sure there are more ways to skin a cat. When I first purchased my van, I was under the impression I would be able to get an aftermarket gas tank, but quickly found out this was not the case. Several sources recommended I swap over to a Jeep fuel tank, but it seemed to be more of a pain than anything due to having to source parts, modify sending units, and making a different brand work in a Ford.
Please feel free to share this on Facebook as I do not have one. This is a very straightforward install with little fabrication and I feel, is easier than a Jeep conversion.
Using measurements taken off of my van, I was able to conclude the third gen tanks are pretty close in size to the mid Ford tank, just a smidge bigger. There is a difference in location on the filler neck. Mid Ford van tank filler necks are located in the rear driver corner, while the third gen tank is located in the middle of the driver side.
You will need:
A 90 degree pipe bend for exhaust pipes. One end should be 2" and the other should be 2 1/4".
Flex fuel filler hose in 2 1/4" openings. Most places sell by the foot and it is about $25 a foot. You will need to cut to size.
Specra F15A ifuel tank. The fuel neck size is approx. 2 1/4" wide for the new tank. The original tank has a slightly smaller neck of 2", this will match on the filler tube where you pump gas.
Spectra FNH012 filler hose. One end will be 2" and the other is about 2 1/4" wide. At this time, you will also need to replace your fuel sending unit with Spectra FG72A. Your existing sending unit wiring will hook up to this unit. You may need to use a Phillips screwdriver to widen the contacts on the plug to fit the new sending unit, but it will fit.
A barbed hose splicer in 3/8" to 5/8".
Because the new tank is slightly larger, the tank straps will seem too small. You can reuse them, but will need longer J hooks. I purchased a large U clamp and cut it in half. Using heat, I bent them into the right angle.
Here is the new tank for comparison. It will fit into the old location. Make sure you use a form of insulation between the tank and the body. Jute works well, I used some old rubber mud flaps.
Install your sending unit.
Test fit the tank a few times and see which position works the best. Your tank straps won't line up in the tank grooves 100%. One strap will land on the raised area. This shouldn't hurt anything.
Your old filler hose will pass through the frame. Remove it now, but do not cut the tank vent hose. The vent hose is 3/8" fuel hose. You will need this. The Spectra filler hose will clamp into this location. The hose will be about 1/4" larger than the filler neck. This is ok, just clamp it tightly and it will not leak.
This filler hose will clamp onto the pipe bend here in this location. This will give you extra length due to the relocated tank neck. Before you fully install the tank, you will need to place your pipe bend and test fit. Once everything has been test fit. Leave in this position and install the flex filler tube to the tank. Don't kink it too much, but you'll have to bend it, unless you find a pre-bent fuel hose in the 2 1/4" size.
Slowly raise the tank into position and measure how much hose will need to be removed. Make your cut and test fit. At this time you should install the vent tube. The new vent tube will be a 5/8" fuel hose. I purchased about 3' of 5/8" hose. You will not use all of it.
Here you will need to get a bit creative. The new hose sizes and the pipe bend will not allow you to run the vent tube through the original location. On the rear part of the frame is a hollow area where there is some wiring. Find a suitable location to drill a hole large enough for the 3/8" hose to enter and exit through an existing frame hole. Once you drill and snake the hose, run it to the new 5/8" hose and use the barbed splicer to join them. This is just a vent hose, no fuel flows through here.
Connect your fuel sending unit wiring and install the tank. You are done. Fill her up, check for leaks and go cruise.