I'm hoping I can save someone else some aggravation and time with my recent experience...
I got a turbo R200 (3.54), and I'm replacing all the seals and fabricating a mount for drag racing this season. I went to my local dealer for Nissan parts and found out I know just a little more about my car than any of the monkeys working there (John Elway Nissan ). I ordered a rear cover seal, a pinion seal, 2 side seals and a stock diff mount. I spent over an hour with the guy going over their computer listings and crappy diagrams trying to identify the parts. They came up with several numbers for rear cover seals, so I ordered both because they wore supposedly both for an R200 . We also came up with some numbers for the pinion and side seals, and got it all on order.
I got the parts in. One of the cover seals was obviously for an R180 (and it referenced correctly for a 280ZX turbo doh!). The pinion seal was correct, but the side seals turned out to be pinion seals (more confusion). After re-ordering the side seals, I finally got in the right part. It took three weeks, all told.
R200 Nissan part numbers:
Rear cover gasket : 38320-N3111
Pinion seal : 38189-N3100
Side seals (2) : 38342-N3100
Stock diff mount : 55415-N4301
Don't go in to get stock parts without the numbers!