[abus319]

Bigben
Since this site is mostly dedicated to preserving these classic old trucks, you might not get much of a response.
I am in the middle of my first frame swap on a 64 C50 to 79 C60 Chevy frame. I will pass along what another member recommended.
Park both trucks on a level surface. Since the front wheels are the most difficult component to move, use the center of the front wheel hub and a level or plumb bob to establish a reference line and mark it on the fender lip. Measure the firewall, front and rear body mounts and the radiator from that reference line and compare.
Also measure the frame width and wheel width to assess clearance. Look in the engine compartments for conflicts like steering column steering box type engine space required etc.
Its a lot of work even when the chassis are similar. Is the pain is worth the gain????