Pham's gets my vote - complex beyond belief to integrate, impossible to package, a cantankerous engine, and it will cost a fortune to tune up. But as an alternative, having the sibling W8 would get you all of those problems, but at a lower cost to acquire if you can find a VW Phaeton in a junkyard. You could even mount it in the cargo area using the FWD factory transaxle for the world's first W8 mid engine Supra.
Heh. Back to reality, I have always thought the Lexus 4.0V8 would be a fantastic swap. I have one and was hoping someone would hit and total it until I changed my mind when the frozen 7M in my project car finally freed up after 3 months of Kroil in the cylinders.
I have two 1FZ-FE's and they are monsters. I'd be curious if they fit in a Supra? It's an industrial engine that also sees duty in forklifts and industrial stationary pumps. It's huge and weighs about the same as a GM 454 block. Great engine.