Can anyone confirm the differential model that I just pulled from my Z? Seems like an open R200, but I'm not 100% certain. I have to replace the cover gasket on it. I'll be replacing the oil, changing the gasket and cleaning/painting the casing. Anything else I should do while it's off the car?

Yes, that does look like an R200. The rectangular piece of metal under the drain plug is one of the things I look at, along with the curvature of the bottom (of the diff). And the lack of a bolt-on side cover for the half shafts. What car is it from?

No idea on what else to do while it's out, I've only swapped old diff for old diff, for ratio reasons. The side seals seem pretty easy to replace, from what I've seen. That thing is very greasy.

Yes, that does look like an R200. The rectangular piece of metal under the drain plug is one of the things I look at, along with the curvature of the bottom (of the diff). And the lack of a bolt-on side cover for the half shafts. What car is it from?

No idea on what else to do while it's out, I've only swapped old diff for old diff, for ratio reasons. The side seals seem pretty easy to replace, from what I've seen. That thing is very greasy.

It's from my 1976 280Z. Dunno if it's original or if the previous owner swapped it out.

R200 is the standard differential for the manual transmission 280Z.

I would open up the FSM and see what it says. It has a whole section on rebuilding the R200. PD chapter. Take some measurements and see how worn it is.