the engine blocks are different. The B6 engine's thermostat is different, it is electronically controlled, where the TT one is "normal". The Coolant passage where the thermostat bolts is different. And the TT block is webbed. But they will bolt into the car the same
Correct.
I am pretty much just using the AMU block and head. All the external accessories will be off my AMB engine from my B6. I'll most likely retrofit the B6 thermostat to the older style like what came with the AWM.