Looking for NA 1.8 BP short block assembly in the Boston area. A 9:1 compression built block would be ideal.

 

It might help you letting you know there's no such thing as short/long block with the 1.8. They're all pretty much the same from 1994 to 2005. Any would fit in your Miata. It would all depends on the sensors depending you have an OBDII (96-97) car you'd have to take from your old engine to the newest one if you find a 94-95 engine which are OBD1. For the 99-05 engines, I can't help much tho.