Lets go about this a different way. Find documents on a car or truck of equal weight and back fill your program with that information. If you have hard numbers from the manufacturer, won't the pressure still apply to your truck? It will be easy to measure the pedal ratio and from there figure the travel amount, that should be the only difference. Rear lock up is going to be different on every truck due to tires, road, adjustment, shoe grade, drum surface, etc..... so forget about figuring that in. In worst case, you have to install adjustable valve to limit rear application.
I suspect the pressure you are after can be obtained several ways, either from master cylinder bore size, caliper bore size, or wheel cylinder bore size. I suggest looking a kit already made up and sourcing parts from it.
When looking for disk for my truck, I found a GM car of equal weight and length that used the same type of disk. The rears are standard drums ( close enough ) to original car I pulled parts from. The proportioning valve worked just as it should have and pedal effort is what I expected for manual disks. No surprises at all since I choose components from the correct car. I did install an adjustable proportioning valve to limit rear brakes due to lock up, but then that was also expected, trucks always lock the rear brakes.
Joe
