I have seen motors mounted forward, backwards(yep I know a few US racers doing this) and sideways.
Some guys like the extra weight over the front axle, and me, I like the weight centered towards the middle(just me sayin).
But I did hear something about the engine may not cool properly when mounted backwards?
...can't remember where I heard that - don't know that it's true.
IT REALLY SHOULDNT MATTER WHAT DIRECTION ITS MOUNTED IN AS LONG AS ITS NOT UPSIDE DOWN.