You may not be worried about drivetrain, but a four-speed did not come in the Early Broncos - a three on the tree was your only option for a manual. I've known people to put NP 435's in them and make it work, though...
Im now emailing a guy with a 79 f100 it seems like a good deal there's about 5 trucks im looking at now and I found a guy that said he can fix the frame on my 80 for around 400 bucks ill post pix of what ever I go with