Call Martin at Monster to answer your last two questions, there are variables and he is the one that can give you the definitive answer......I believe there is a carb legal swap in the ls section using a GTO donor swap, shouldn't be to hard to find it since it just passed carb and ref recently. He did have some hurtles but made it threw.

 

To add to what Hotwheels posted, you might want to look real hard at what year Miata has to jump thru specific hurdles to get emissions certified in California as it seems that I was reading that it is much easier for 1994 and earlier cars to get certified.

 

Here is the Carb build....

https://www.v8miata.net/general-moto...og-2942/page4/