In order to properly turbocharge the P11 G20, you would need to obtain an OBD II wiring harness and ECU and have JWT reprogram the ECU. For the kind of money you would spend on the labor to make this wiring harness work on your chassis, you might be better off going with a stand alone engine management system such as the GReddy E-Manage. I would recommend turbocharging the existing SR20DE engine. JWT makes S3 cams for the roller rocker head as well. Don't turn up the boost too high on this motor though, as the CR is 10:1 and the main bearing caps do not have a girdle.

Good luck,