OK makes more sense now! I assumed a center diff just because I'm used to my buggy being off-road, forgot a lot of people use a locked spool or 2-speed for GT.
I personally chose to have the motor in the front left because that was my previous setup, and I have all 2S hardcase packs for a saddle setup. It wouldn't be very hard to flip around to right rear and have a single pack setup.
If you put the motor on the left rear you might be limiting your battery tray size a bit, because you would have the servo mount up front, whereas on the other side there is nothing all the way up to the steering post. But I think there would be enough room either way, just have to move the ESC around a bit.