489 Differential Case

I understand AJ, I'm working on 2 different projects. And if I'm reading the technical info that I'm reading correctly, the open carrier or Sure Grip all, 8.75 ring gears will fit any "case", but the 741, 742 and 489 pinions will only fit there respective case. In this case, no pun intended I need a 489 case as I have all the parts to rebuild it from Dr Diff, but the one I have is not serviceable.
I just stumbled upon the 742 set-up when picking up some other parts and at $80 it seemed like a bargain.