I put a 50 cab (48-57 are similar at the floor level, I've had a few between 50 & 56) on an 80 short box 4x4 frame. The 50s cabs sit forward on the frame more then the 73-93 cab does, and the 50s cabs are not as long, front to back. The firewall-wheel well-radiator support is at least 6" shorter on the 50s front end and the 80s frame horns need to be cut off. The nose of the 50s sheetmetal needs to \sit right against the front frame crossmember, and that still puts the wheel well in the wrong place. The engine will sit about 4"-6" in side the firewall on an already short cab. I raised my cab 6" above the frame, makes the truck sit high, but was easier to deal with.

If your planning on doing a step side box, with the cab shifted forward on the frame, the box side wheel wells are just in the wrong place, weather you have a short box frame or a long box frame. These are not easy swaps. Here is a picture of my 50. A Dakota frame fits much better under these trucks. Gene