Two more questions:
1. As you state that the coolant channels are completely different, then that means that there isnt a way to modify either the block or the heads to match up the channels of the other part of the engine? IE modify the channels on an EJ18 block to match the EJ20 head, or modify the EJ20 head channels to matt up with the EJ18 block? Or is it that they are in such completely different locations that it would be impossible to do?
2. You stated that the WRX EJ20 heads are designed specifically for turbo aplications, so even a WRX EJ20 without the turbo (kept in N/A form) would not work well as an N/A motor even with cam, valve, piston, crank, etc. modified parts because of the fundamental design of the WRX heads to flow best with turbo use?
Bonus question: I was talking about this subject today, and wiring harness issues were brought up. If an older block designed for OBD-I wiring was matted to a newer heads that were designed for a newer OBD-II car, would there be impossible issues with the wiring or would it be overcomable?