Quote Originally Posted by GKR_17 View Post
You don't if you want to be legal.
I don't know much about the E36 diffs (but ask me about E30 diffs ...), but I would think that they would be the same diff case as each other, so it should be a legal swap.

You probably just need to swap the output flanges between the two diffs. They just pop out. Take a long screwdriver, position it between the output flange and the case, and give it a little pop. Just swap the 318 flanges for the M3 flanges.