Shaft Length
If you see ↓↓this↓↓ shiny-looking button when you look inside the diff., they're still in there:
I couldn't tell you which ones have it, or don't. It's only needed if you have the old style adjustable axle bearings. And then you'd certainly have to get the axle lengths correct. But you don't need to worry about it. The thrust block, or "buttons" come out without disassembling anything. The two buttons are held together with a roll pin. Easy to drive it out with a punch, then the 2 halves separate and you should be able to slide them out.
If you see ↓↓this↓↓ shiny-looking button when you look inside the diff., they're still in there:
