Just thinking out loud and someone may have already answered this BUT wouldn't a Supra TT head bolt up to the Lexus L6 block? This would allow use of the factory TT exhaust manifold and turbos and or any other Supra parts. The head may have larger combustion chambers which would allow more boost and may have turbo optimized camshafts. Of course a Supra intake and plumbing would probably be necessary. Again, I have no idea how available/affordable this would be.

What's up John.
Scot here,
well like any good SC owner of the NA 3.0 L, I have checked into this, Yes it would make it almost too easy for mods, but unfortunately they dont fit, they bolt up, but the cooling passages are all different and so are the oil passages. I spoke to Jeff Watson at JayMarks, he told me all this. Also told told me that the coolant runs in opposite direction of NA block(?).

I think the NA head is good, perhaps better than the TT head(flows better), just no aftermarket turbo manifolds for it(tubular).

Scot Hail