GTS is trying to boost numbers here in NorCal and would welcome your car. You'd have to look into their rule set as to which GTS category you would fall (944Spec cars are GTS1). I'd guess GTS1 or 2. Most of the GTS cars in Norcal are SpecE30's currently and both they and the 944Spec can supersize into GTS.
Alternativly as Ken said -- pick up a cheap 944 or 924S and come play with us.
(Either way come play we'll still welcome you)