yeah it's been done. the porsche boxster IMS recall means there are a lot of lumps being junked out there for owners who can't afford a $20k + repair bill. since it's the poor mans porsche, you can probably get your hand on any number of maybe ok donor cars that you could steal for a mechanic's special price.
so after you replace the affected parts, all you need to do is fab an adapter plate for the miata transmission and make your own mounts.
should make for one badass ride man, can't wait to see your build thread.