[dsraven]

Decide what you want to do with thr truck, rusty patina look with a newer style underside or something straight and smooth with a newer style underside etc. That will help you determine what sort of truck is best suited. If you plan on smooth and painted then look for the best body you can find or simply plan on replacing panels. If a newer style underside is wanted then the original driveleine isnt even needed. The cab is probably where most of the body work will be required so try to get the most solid cab you can. If something absolutely awesome and new is what you want build a truck from nnew parts. Not gonna be cheap to go that route but entirely possible.
Figure out what you wanna end up with and go from there.ic hanving a whack of stuff on the underside so you have ifs and fancy rear suspension then all the original stuff becomes irrelevant except for the actual frame, or maybe not even that if the plan becomes so involved you will replace the frame too.