The diffs I used synthetic 75-90w gear oil.
The trans and transfercase take 50w. It used to be fine to use the same gear oil as the diffs since it was the same viscosity.
BUT, the new GL5 standard that is in the gear oil (try to find a synthetic that is not GL5) will basically eat the "gold metals", copper and bronze. Since the trans has those in it for synchros, it could be bad for the trans. So I used 50W, and it was hard to find at a box store, only one brand and quart bottles.
I picked up a $10 harbor freight pump that screws on top of quart oil jugs, worked great for the trans. The others you can get by without it.
I had read about the GL5 on here, and asked my favorite parts guy and he completely agreed, so I went with the 50wt oil. I have no other experience regarding that.