I'm pretty sure you could do a 302 conversion and have a good balance, you can do it in a focus, so probably can in a miata. The miata engines STOCK were made for small amounts of boost. A friend of mine ran ~10psi daily on a stock miata engine and ran 14psi for a while until he totalled it. They can handle more power than you think. Hit up the miata forums and you'll see.
