If you are going to use an '04 ECU you need to use an '04 harness, or do some rewiring.
There is quite a bit of wiring you are going to have to do in any case, because the 2.5i does not have the fuel pump controller like the turbo models do, along with a bunch of other differences.
I recommend downloading the wiring diagrams and figuring out everything you need to get before buying anything. That way you know all the parts you get will work.