I recently bought a 91 318is and one of the first things I noticed is the need for a LS diff. My 87 535is has one and I love it. Anyhow, what diffs fit? Only ones from 4 cyl 3 series? Or do ones from 325's fit? Also, I'm not sure of the ratio of my stock 318is, so what's the best for street use? Thanks, John