Do you know what the bore size of you current motor is version the bore size of the engine that those heads came off of? When people do the 2.0l WRX heads on a 2.5l turbo block, there are problems then just the raised compression ratio that happens if you keep the stock 2.5l pistons and run a stock thickness headgasket.
I don't know if there are any problems with your 2.2l combo though. Here is some info on the 2.0l heads on a 2.5l and service to fix it.
http://forums.nasioc.com/forums/show....php?t=2011458