Sounds like a Major Major job. If using a patch from a donor cab, or if removal of those three screws and welding/bolting a patch, could very well affect the alignments of the cab to the frame, thereby causing door, rocker panel, front fenders to cab and running board alignment problems. Not sure why they made the joint like that. Could be for cab flexibility over rough terrain? For me, it would be like a Rubik's Cube on reassembly.
Just my thoughts. For a metal expert, may be no problem at all.
Dale
