I have the chance to get a good deal on 3 pick ups. 2 1972 crew cab short boxes 2wd and 1 74 regular cab long box. If I buy these would it be possible to get a crew can 4wd out of them? If so how? I don't figure the crew cab will fit on a reg cab frame but I might be wrong. The goal I have is a 4 door short box or long box 4wd and then do a cummins swap in the future. Thanks in advance

probably be easier to swap a 4x4 suspension off another 72-80 Dodge Truck onto one of the crewcabs & you'll want a short bed crew as they look better than a long bed crew. my

Yes, swapping in the 4wd crossmember and spring mounts to the crewcab frame would be the simplest way to go. Just buy a running 92-93 4x4 and move everything over.
I did this with my 2wd crewcab and it was the slickest swap ever. Nearly everything was a bolt in.