just remember that if you plan on running an age class you will be against EVO3 on anything beyond Vintage at most events. I always tell people - Yamaha and Suzuki - up to and including 84 bikes, Honda - up to and including 83 bikes, Kawasaki - up to and including only 81. Maico, KTM, etc just make sure no disc but I think they all stop at 84. AHRMA has 4 races in the area, to include Redbud Labor Day that will follow this structure with different names. They just call it Ultima, Grand Prix, and Historic instead of EVO3, 2, and 1. You can find this info at
www.ahrma.org No disc on either wheel and the only power valve allowed is Yamaha to 1984. You can not retro a later bike to not have a disc either. AHRMA only allows the NC stuff at select events but I really think that will be changing before long. Others may differ but you can't go wrong with an 83 CR, 82-84 RM, or an 83-84 YZ. There are a good bunch that swear by the air cooled still and they do win. If you ever see me at a practice track just ask you are welcome to take my 83 for a spin........