Use your wiring harness from the car now. Dont get another and make it more difficult then it has to be. Buy a obd2a to obd2b ecu jumper harness to use the p2t ecu. You can use the si harness to get plugs and wires and such that you will need to make you stock motor harness work.

 

Use your stock harness, only thing i think you have to wire in is the V tec and its 3 wires i beleave just look on honda tech or civicclub for the pin out on it and run wires to the empty spots on your harness plugs and you'll also need the OBD2a-OBD2b adapter. Theres really no point in using the si harness seeing how its OBD2b and the cabin is setup diff.