I have proposed a restructuring of the novice classes to deal with this very issue. The idea is to have Nov-A, Nov-B and Nov-C instead of Sportsman, Nov-U and Nov-O and have lap time limits for Nov-A and Nov-B, like is currently done for Sportsman. The slowest riders would be eligible for Nov-A, faster riders for Nov-B and the fastest for Nov-C. Slower riders could ride in the faster classes if they wanted to.
I think this makes much more sense for the novice classes than doing them based on engine displacement, since lap times at this level are much more dependent on the rider than the bike. I'm curious what you and other potential new racers think of the idea.
Dirk