My opinion is that you would do well for yourself to keep the avcs, run the engine with it's matching ECU and modify the harness.
Romraider support for your turbo and the V7 is not a problem.
You could ask Steve at IAP for the wiring manual of the V7 engine, and get the wiring manual of your chassis, if you don't have it already.
Then buy USDM WRX wiring harness components as needed and get this done.
There is a lot of knowledge and help available in this thread.