The first thing you need to do if you want to use the original COPs is find out some details about what inputs the northstar COP setup needs, is it a 5v trigger or is it 12v, ie is it "logic level" or "high level", then you need to either find an ecu with the correct number of outputs of the right type, or find a way of retrofitting something like the EDIS setup which can convert between the two.

If you dont mind changing which type of COP you use (ie not mind the cost of buying different ones and potentially having to pay money on machining to make them fit), it will open your options up more.