You dont want the SOHC heads from your 2.5i
Get WRX or STi DOHC heads. If you do this then Agile will most likely not have an issue. You still will need a DOHC harness from whatever motor the heads cam from. I believe your stock harness that comes out of the fender that connects to the motor harness should plug into the new harness ( as long as its close to the your year ) , but it will have to get repined and a few wires added most likely.
If you where to stay with your stock SOHC heads you should go stand alone EM. Also you will have quite a hard time finding upgraded valve train bits to wind the thing out to 7k+ In addition to that the SOHC heads dont flow very well if you are going to be putting a 30r on there.
I have delt with Agile and Hill and they should tell you basically what I just said.