Dumb question:

If I had a v8 JDM EJ207 long block and wanted to test it for a while, could I swap the entire intake manifold from a 05 USDM STI motor to the JDM 207, drop it in and control it with the USDM 32bit ECU assuming that the ECU is tuned correctly?

Again, keeping the entire intake manifold means that the injectors, TB, Drive by wire, etc all get retained. The only thing that I really worry about
is the AVCS control but for all I know it could be totally incompatible. Thanks.

you could swap everything right over...but you need to get tuned like you said.

So the USDM STI AVCS control is compatible with the JDM variant?

I am NOT sure but my guess is that you would need to use the USDM heads to retain the USDM ecu, thats how it usually goes.

but I MAY BE WRONG!!!

no, you are right
it's way too complicated to make this work, search for it, it has been brought up before several times