Dont buy a Centerforce. They are not nearly as good as Spec clutches are. Search Corral.net forums under Centerforce, theres like a 10 page discussion with unhappy Centerforce owners.
Spec clutches are far superior to centerforce. At least thats what I've heard time and time again. I ordered a stage 1 last week for $189. That beats the price of almost any aftermarket clutch out there.