Snail,
IIRC, FIM rules are for displacement only.
I.E.; if your motor is larger than 1350cc, you get to compete with anything larger. (Such as the current world record holder @ 322+.) And I think there's an extra fee for FIM certification, and advance notice needs to be given, etc.
It's been a couple of years since I looked at the FIM rules, so read those 200 pages carefully.