I haven't had any problems and have seen quite a few riders do so. As long as it is securely mounted, you shouldn't have any issues. This video is from a mate's bike (Jamie Devine) which is from the March meeting at Anglesey.
if i were you, cut your losses, sell the trackbike and buy a package that is ready to go in the class you want! prob wont work out much more money....
Hmmmm, would it fit? In my opinion, I would sell the 750 and start from scratch. I think it would probably end up being more expensive in the long run to try to swap engines over. I would say that your 750 won't have lost much in value, so sell it on and try to get a good 600.
Yeah ive got 2 years to sort it out if im being realistic about it. Gonna get some more trackdays under my belt first!! I wanna do one without falling off next..