I'll go ahead and touch on a few more things. I'd like to do some gauge cluster rebuilds whenever I can get my hands on some, and maybe even a steering column, but until then hopefully some of this mess will help some folks out there.
These are shots with the dash removed. It's a disaster of dirt, cobwebs, insulation, brackets, wiring, and junk under there; but you can see the two braces that run from the doghouse area to the kick panels. Things like the e-brake assembly and the brake pedal assembly are bolted to these structural braces to help strengthen everything up. I found that once you remove those two braces, it's much easier to get at the things like pedal assemblies, heater box, and all the other goodies you might need to get at under there.
So the first thing I'll go into removing is the brake assembly. The brake pedal has a contact switch that works when you depress the pedal. The switch mounts so that when you press the pedal, the switch plunger releases and makes the brake lights turn on. Remove the switch and you can move on to the rest of the pedal assembly. You can see the white cylindrical switch mounted to the pedal assembly above, but I'll try to get a close up from my 82 when I get a chance.
The brake pedal itself is held into the mounting bracket with a pivot pin. There is a spring clip on the passenger side of that pivot pin. You can usually just get a flat blade screwdriver under the clip and gently pry it off. Then push the pin through to the driver side of the assembly being careful not to loose the two pin sleeves on each side of the assembly. You can see the clip in this pic.
Once you've removed the pivot pin, the pedal itself should drop down, allowing you to remove another clip that holds it to the rod that actuates your power booster or master cylinder if you don't have a booster assembly.
Next you can remove four nuts that hold the brake assembly bracket to the master cylinder or booster if you have one. The bolts will go through the firewall. Then there are two more bolts at the top of the assembly that hold it to the firewall. Once all the bolts and nuts are removed you can remove the assembly. It takes some wiggling and twisting sometimes, but be careful if you decide to strike the studs with a hammer as you can mushroom the head of the studs and ruin the threads.
The e-brake is essentially the same procedure, except it's not connected to a rod that goes through the firewall, but instead it is connected to a cable that operates your emergency brakes.
The heater box is pretty straightforward to remove. You simply have to remove the two heater hoses from the heater core on the firewall side. Then there are a handful of small bolts (1/4" if I'm remembering correctly) around the box and ductwork. Remove the ducting first, it will save you a bunch of frustration when removing the box. Then you just gently lean the box into the cabin and pull upward being careful not to bend your heater core tubes or damage the fins (if you're reusing it).
One of the heater control cables goes to the blend door in the heater box. I didn't photograph this process, but can edit this thread when I do the one in my van eventually. That one is held onto the heater box with the end of the cable coiled into a spring like shape and slid down over the blend door shaft.
One area a LOT of folks neglect is the crotch coolers or kick panel vents. Over the years all of the debris that makes it past your wiper cowl and into the cowl vent area eventually works its way down to the kick panel as that is where the kick panel vents draw air from when you open them up. Here you can see the typical pile of nastiness that makes it into the wiper cowl area.
And here is the driver side kick panel vent. The vent itself is just a plastic trim ring with 1/4" sheetmetal style screws holding it into the kick panel. Then the flap is held into that trim ring with a vertical shaft. The flap in this 75 Beauville was made of metal, but had some foam around the edge that was WAY overdue for being replaced. The down inside the hole you can see the pile of leaves, pine needles, etc that like to work their way down there and hold moisture. This is a common spot of metal rot on the 67-72 C & K series trucks, so I'm sure it would be a problem area in the vans that a lot of people overlook as well.
If you don't want to disassemble all of this stuff at least stick a vacuum hose down in the kick vents and vacuum them out on occasion.
Bonus tip for today. This little floor mounted high/low beam switch for the headlights is exactly the same in the 67-72 trucks and has caused me more electrical gremlin headaches than any other part. Since it's mounted on the floor it tends to collect dirt, mud, moisture, and all sorts of mess. Then it will cause all sorts of random electrical problems with your lights and other components. I've spent hours trying to diagnose weird electrical issues, only to swap this thing out eventually and solve all my issues. I always try to keep these clean and replace them when they look worn or funky just as a cheap piece of mind.