The most common is the GM D44 w/4.10's (a 10 bolt is essentially the same thing, but used a wider variety of gear ratios). Dodge also used a D44 w/4.09's, but they're only 5 lug.
Waggy 44s are also a option. Late '70s are pass side diffs. I beleive they went to driver side diff in '80. Be careful, depending on the tcase, so of the rears are also offset. But you may be planning on keeping the toy rear?
I don't know yet. If I can find matching d44's then I was going to use both of them. Then maybe a 60 rear later on. My ifs is just not cutting it anymore.
With waggy 44's you will still be outmatched with a 60 rear. The waggys are close to the width of a TJ so you would need to find a narrow 60 to match or go ahead and full width the entire thing now.
I agree with the rest of them...Toy stuff is pretty tough these days. What size tires you planning on running? That will help determine what axles. Me and my buddies are running up to 39.5 Irocks on toy running gear and loving the ground clearence. We are pretty rough on our toys... Broke one set of steering studs last weekend with the 39s, (no shafts or gears)
If you think you want the 60....save the money on doing things twice and go ahead and get a 44/60 combo out of a older Chevy.