I would expect you would have to move out away from the case with a short shaft & support bearing to run a belt drive. If you wanted to run a bigger chain & sprocket setup, the same would apply.
I seriously doubt that reliability would be an issue with the appropriate size belt.
There is a bunch of that stuff for Harleys on the market, but I'm not in that playing field.
With small engine classes in any motor sport, you need to go after everything you can get.
Sid.