if you want to leave the diff in the case you wil need to replace the rubber bushuings up towards the yoke with solid ones, also the rear cover will need to be swapped for s13 rear cover. also after replacing the bushings, you will need to source longer mounting bolts for the front mounts, and find some big washers to shim the diff case or else it will hit the subframe. the 300zx diff and case is alot beefier i have it in my car, we dissasembled it before installation and found that the pinion gear is about 1/4 in larger than the s13-
should handle alot more power
