Unless you have a 93 or a 99+ I believe all Miatas are 50 state.
The 93 has sequential fuel injection via a different ECU and wiring harness, where as the Fed cars of that year model do not.
The 99+ Miatas with Cali emissions have a pre-cat and a regular catalytic convertor. They also lose 2hp but have it peak 500rpm earlier.
Probably more than you wanted to know but oh well. I'm a fountain of Miata knowledge.