The 2wd trans is a two piece housing, and it splits halfway up from the back. You're almost replacing half the trans at that point and still rebuilding the tail section. You might as well just rebuild the 4x4 and not bother separating the two trans. After all, once you get even one back together, you've done about the same amount of work as a full on rebuild. Especially if you replace the front pump seal as recommended whenever you have an old trans off the engine. I'd also strongly consider inspecting and replacing the torque converter, its possible that is old and worn out as well and could be part of the cause of the trans failing.
