Yes, LSD from S13Ks should fit 180sx... take note of how many bolts your output shafts have, though. Some late 180sxs had 3 tab, 6 bolt shafts. Early models (I think 1995 and earlier) had 5 tab, 5 bolt shafts. You have to make sure the ones with the LSD (assuming you're getting whole pumpkin and not JUST LSD unit) are the same as the ones in your car; otherwise, you'll need new axles.
This gets quite complicated (which axles fit which LSDs, which LSD carriers {"pumpkin"} will fit in which cars...), I suggest doing a search first.
If you're just talking about the actual LSD unit, S13Ks will work with 180sx.
Nismo LSDs are, I believe, Just as good as Kaaz/Cusco/ATS... on the other hand, ATS is coming out with a carbon LSD, which sounds like it'll kick butt. Nismo also has SSS LSD, which is supposedly really, REALLY top of the line. Pros (like Dousan and Dorifto180sx) use it.
