The rules are kinda confusing.
Looks like any 1.6L Miatas, or 1.8L Miatas without an LSD can run in Sport 3 (like STS2). However, 1.8L LSD Miatas can only run in Grand Sport 3... with fewer modification points (450) compared to the 1.6L and 1.8L open-diffed cars, which are allowed 550 mod points.
Looks like my car justs squeaks by under the GS3 points limit in C Stock trim:
250 pts - R compound tires
100 pts - non-standard single-adjustable shocks
25 pts - non-standard front swaybar
15 pts - non-standard exhaust
50 pts - addition of roll bar or cage ( <---- what's this crap? I add 50lbs of dead weight to the chassis in the interests of safety and it counts against me?)
440 pts total.
I'll give it a shot and see what it's like.