His response so far:
Thanks for contacting me. Because the 08+ GR is a CANBUS system, it makes the swap pretty complicated wiring wise. The whole point is to get the GR ECU to work because it can control the dual AVCS. In order to do that you need to make it happy and that really isn't possible unless the CANBUS sees every sensor throughout the car working properly. Your best options is to swap everything over, wiring/dash/hubs/trans/etc. Not sure how the GR dash would fit in a GD, but probably would fit better than the couple attempts I've seen in GCs. I'm working on trying to figure out how to do a GR swap without doing all that, but it's going to take some serious electronic trickery to make the ECU happy if it is merged in like you would do for any 07 or older swap.
Thanks,
Brian
Let's hope he can figure out a solution