This is what we use in our Spec Miata race cars and recommend for your Spec Miata. It is necessary to have a solid hub clutch disc for lightweight and the clutch chatter is almost non-existent on take off, not that it even matters on a race car that lives between 4000-7500 RPM's.
Replacement ACT 4-pad solid hub race clutch disc for ACT kit: ZM2-HDR4
ACT Xtreme Race Discs are available in 4 or 6-puck hub designs that are highly durable and resistant to heat. ACT 4-puck Xtreme Discs engage harsher, shift faster, and are well suited for the smaller disc sizes from smaller engines.