I Need to know what diff's i can fit to my 1987 R31 nissan skyline, would the 300zx lsd be ok? if not what else could i use?

im pretty sure u can put a r33 gtst diff in it.. there pretty good and i think they have a 4.11 ratio

No, the R33 diff is an IRS(Independant Rear Suspension) diff while the R31 Skyline has a live axle. The 300ZX diff is also IRS and uses CV joints rather than a solid axle.

The new Ford Falcon XR6 turbo LSD does fit in the Borg warner diff though. I have a mate with an R31 that we fitted with an R33 RB25DET. You could also fit a VL turbo LSD but the XR6 turbo LSD is a much better unit and is cheaper.