RHarvey,

Look in the Tons O Fun Forum. Pinned to the top is a wealth of information regarding one ton axle swap. I would say 95% of it applies to 3/4 tons also. It is a great resource to start your search. https://www.stovebolt.com/ubbthread.../14-bolt-axle-swap-info.html#Post1249600

Personally I put a 14 bolt axle out of a 2004 HD2500 under my 3600, but I have a flat bed, so I wasn't as worried about width/fenders.

Good Luck
Jon