I finally finally finally did it, I bought a cheap as shit bike ($400 cbr600). I upgraded the front end to a 97 zx6r with my own clamps (I wanted cartridges). and fixed the back (someone put an f2 swingarm on it and the geometry didn't work right) - I had to machine a new dogbone link and move the swingarm link mount a bit to get the right rate, also ordering a slightly stiffer spring as the specs are 130kg/mm and what I've got measures 100. engine runs, brakes work, chopped up the wiring harness to just the minimum, going to fab a quick belly pan next. now I plan on running as many track days as I can this summer, and I'll be retaking my racing license, the whole point of this bike is to ride and race a bike that I absolutely don't give two fucks about, so I can learn how to ride well and only be afraid of hurting myself, not hurting a pretty pretty bike.
Themotoworks,Nothing worse than building a race bike and then finding out it doesn't fit into any class.
I think some of the USCRA CB350 guys have a problem with their bikes fitting into AHRMA classes.
Looks to be a good starting place for what you want to start off doing. Make sure that when you head to tech the motorbike is clean, proper safety wired,good belly pan, shark fin, etc so it looks like you are on top of what you are doing.
Don't worry too much as to what class you will race in. Most sanctioning organizations want you to race so they will help you find a spot where you'll fit in. Our motorbikes have been built to race in the UK and IOM where the rules are often quite different. We do like to run some races here in the States and they always find a spot for us. There are classes for riders over 40 years old,50 years old and 60 years old, There are classes for bikes that are listed as classic Superbike and bikes of 25 years old so someplace there's a place for you. Remember they want you to race and they want your entry fees so they will work with you. Now if you start winning they move you to a different class but we've never been turned away and we've always had a great time.
Track days are great places to learn/re-learn the racers skills but real races are where you will truly get into the swing of racing.