WHat year model ECU do you want to put into what year model car?
Forget anything 06 onwards going into anything earlier. Its all drive by wire and requires a different throttle body, accelerator pedal, and even manifold I think.
SO need to know what year is going into what, it may be cheaper to just buy aftermarket and get it tuned.

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F.B. Racing
01 WRX (STI badged)
2010 XR5 Focus
06 Impreza Hatch 2.0i