If you can find a Dana Type 60 rear axle from a GMC it will be almost a bolt-in swap. Those axles have several good ratios available, 3.73, 3.55, and I believe there's a 3.36 available from Ford 3/4 ton automatic transmission models. Ford, GMC, Dodge, and International all ran the Dana 60 at one time or another. I've got one under a 59 Burb with Ford gears, a GMC housing, and a Dodge pinion flange! It's a 3.73 ratio.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!