RE: Differences in B series
 

Yeah it is a bit confusing, because all those trannys share the same ID code. Yeah you'll want a Y80, S80, or a S4C/Y21 should do the trick also. It's kinda strange how the OEM LSDs are priced. If you order them by themselves from a website they'll charge you $1000. If you buy them w/ transmission they'll cost about $1000-1300 on ebay. But if you order them from an engine importer they'll only charge $300-$400 for them (with engine purchase). That's about all I can tell you, as I've only briefly looked into B-series platforms.

RE: Differences in B series
 

the reason i say SiR head is because its compatible with a lot more OE parts than the LS. you can use valvetrain and cams from ITRs, CTRs, GSRs, and any other SiR and get some pretty bitchin combos for N/A or FI (take your pick) and are great for dual duty (meaning achiving most possible power for the track while staying streetable). also it has a lower compression than any of the other 'type R' (meaning ending in R) so is the best for boost of the four. i know it also flows better than both the ITR and GSR and can be ported every bit as much as those two (im not sure about the CTR ports because i dont know **** about the engine or the head, and quite frankly dont want or care to).