I don't only sell parts...
My car before.
Friend's car...
And yes you have to shave the block.
And yes, the scion TC manifold will fit. once the block is shaved.
IC does not fit easily. Had to shave the front support and delete my windshield fluid. I'm sure you can get creative and not do both, but it was difficult.
AEM piggyback was used.
T3/T4.
i pushed out 330WHP for a long time on a healthy tune, with good AFR across the board.
I have an auto. Tranny was and is still healthy.
My friend pushed out 390WHP. He had a manual.
Hope this helps in getting some good ideas in your head.
Good to know we have some tuners here (and knowledgeable according to your experience in subarus)
To be honest, I sometimes get tired of helping people because they're all talk. If you really are interested, I'd be glad to share my wealth of information to you and help you get started. PM me if you want more info. Best of luck to you.