The engine and torsen are the main value. Tranny is pretty common and prob worth a couple hundred bucks, maybe three tops.
If the motor has good compression numbers and reasonable miles, probably worth $600ish. Including ecu, wiring, etc? Adds value.
I think the going rate for a torsen (diff, housing, stub axles) is around $700, give or take. If it is a type 2, maybe more. Again, miles and what is included will affect the price.
Are you parting out the entire car, doing a V8 swap? If so, you can make the most $$ by packaging those high-value items with the needed accessories/parts to swap them into older miatas, which is where you will find customers. (me, for example )