What Hoov said is correct but ill shed some more light on the subject also. Some say that you need to make some spacers some say you dont. I am currently running a 3.54 out of an 82 zxt with a lsd out of a 300zx and i am actually not using any spacers. The bolts are not what centers the ring gear on the carrier. And the Clamping force is enough to keep the ring gear from spinning. I recently took mine apart and it had not moved and thats with launching hard many times at the strip and doing 12sec passes.