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The pistons will be different - not sure if the rods are different between WRX and NA (the WRX ones look pretty flimsy, so who knows if they use the same rods in the NA as well)...
Not sure if it's got all the same oil feeds etc, mind. I know some STI cranks have improved oiling, but don't know if there are NA / WRX differences (I doubt there are any differences, but can't say for sure).