See here - viewtopic.php?f=9&t=10920
Only 3 wiring changes needed:
1) Splice wires on auto connector to parking - this is to start the car.
2) Connect speed sensor
3) Connect reverse sersor
Speed sensor is critical, without it stock ECU will be in limp mode.
You can leave twin cat downpipe as well. Only 1 O2 sensor will be working.