I am not an official but I am a rule book geek.
As I read the Super Street rules I'd say your MX5 would still be able to run in SS. It is still Tagged, Insured and has the full complement of street equipment (wipers, horn, etc, etc), right? I'd bet that most of the cars that have been setup to run Maxton in SS or RS have any number of parts that aren't CARB certified and are labeled for racing only. The Super Street rules specifically (reading the 2007 and not the 08 rules here) allow "Multiple Carburetion, Fuel Injection, . . ." etc., etc. So the IRTB setup should be OK . . . BTW your car is also legal for the GT and MS classes.
Maxton records you could chase are:
G/FMS 116.559
G/GMS 139.124
G/GT 139.925
G/FSS 126.424
G/GSS 129.247
See ya at the track in three weeks . . .