I'm not sure about the "3 part number" thing, but yes, 3/4 ton and 1 ton drums are incredibly scarce items. We've got a few professional number crunchers on the site who can not only trace a part back to its original source, but they can probably tell you the Jockey shorts size of the guy who built it! Somebody should be along shortly to give you all the information you never wanted to know about your drums.

Yes, it's possible that people have swapped out entire axles, not only to resolve brake problems, but also to get a better selection of ring and pinion gear ratios. The GM Corporate 14 bolt axle is a popular swap, and it's fairly available at a reasonable price.
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!