Not in my experience. I'm not saying it's impossible but I know that in the past I have removed JDM WRX (non STi) and plugged directly into Aus spec WRX and roared off into the dust without a care in the world.

I would say go back over everything you have fugged around with and make it back to stock. Cambelt done? (if so who did it? I have seen numerous cambelts out of timing)