Ignore the claiming rule. Pretty much obsolete & has been banned by some race organizations. I don't believe it's even enforceable. In any case, no one is going to want your bike. As for the racing. Do the trail riders class first. In this series the age classes, Vet, Senior, Super Senior, etc., are filled with seasoned racers. Even some of the +50 guys are turning laps faster than the younger B riders. If you doubt that check here & look at the lap times from last year.
http://www.racer-results.net/results/gncc/2010/results.asp The fact is you can sign up in any class you want. You'll just finish we you're going to finish. That is why the trail rider class makes more sense. Personally, if you've never raced at all, I suggest hitting some local races in your AMA district or CRA, etc. It's cheaper & you'll gain experience. If you're anywhere near district 5 it looks like they are going to have a full schedule for Hare Scrambles this year. And last but not least, relax & have fun. Your not going to be the next David Night or Shane Watts. And you have to work tomorrow, right.