The following link is to the most up to date SCCA General Competition Rules document including Spec Miata. There are several changes including:
Bushings
Jacking Points
Minimum Weights
Restrictor Plate Sizes
Engine Modifications
These changes apply to WCMA competition for 2015.
http://scca.cdn.racersites.com/prod/assets/2015%20GCR%20March.pdf (http://scca.cdn.racersites.com/prod/assets/2015%20GCR%20March.pdf)
It's official:
QuoteIn SM, Mazda MX-5/Miata (90-93), change the weight as follows:
2300 2275 or 2315 2290 With Alternate Bore
Chris