Very quickly....
All 33 GTS-Ts are Type-M.
GTS is NA, GTS-T is single turbo
Spec 1 - Earlier version than Spec 2 (can't remember the dates off the top of my head). AFAIK the Spec 2 is just a facelift.
There's loads of other variants - the search function is your friend. Also loads of background over at skylineowners.com.
