The frames from 63 to 87 will swap if my memory serves me correctly. I don't know all the details on it, but I do know that the later axles are a little bit wider than the 63-66 frames and the cab mounts are different. The later frames 73?-87 will give you front disk brakes and power steering. Try searching the engine and driveline forum on 63-66 frame swap. Someone will come through here and probably correct me...
