As I see it, and I could be wrong, the only difference would be that the belt tension during forward motion would be on the bottom of the belt loop instead of the top...
I just put a GTC TAV2 on a Honda GX390 and had to put it with the driven (Little sprocket end) facing the front of the buggy. It wont go on the other way because the cooling fins are too big on the 390. It pissed me off because the motor sits a little bit too rearward transfering more weight than I wanted over the back. Serves me right for being greedy and not getting a smaller motor!!!! (LOL).
I have that same problem with my TC contraption nightmare. It's a short backplate so I had to mount it forward because I didn't feel like taking off the motor mount plate and raising it. The bearing sleeve on the backplate hit the motor.