Hey, Stainless, thanks for reminding me that I forgot all about the bodywork part of the rules -- that'd move one from modified into altered. I'm still earning my stripes -- gotta be more sure that I've reported all the rules before I click "send".
Yeah, Bryan, look at the bodywork rules for altered vs. modified. And while I know you're going to ride naked, but you can have the tailpiece on the bike and still be in Open class, so a tall tail section could put you into altered, too.
Probably something else as well, but I don't have the time right now -- gotta go move some more snow.