I would agree with Ethan except for 2 things... 1. You bought the car with the engine... 2. Thats friggin awesome.. lol.
I was going to try a small block in a 73 Celica once, but after mapping it out, figured that the first time I stepped on it, the windshield would pop out from body twist. Thats a very interesting engine swap and cool to see (ty for the pics). But it seems to be quite a rare event as the car can be modded to very high hp ratings with the stock engine (probably outperform the v8).
The only guy I know who would be able to answer your questions (and probably would do it) as he races Supras is at this web page:
Riemer Consulting Technical Services
Hit the contact button and fire him off an email... if anyone knows, I think he would.
Have you ever had the car dyno'd to find out what kind of performance it gives on paper?