skabeeb, you want to get hooked up with AHRMA. the 400 can run in the sportsman 500 class, (up to 75, also age classes). I also run a couple of 74 KX 450's in AHRMA.(cover of the 96 rule book) :cool: I am currently stuffing one of the 450 motors into a 78 250 frame :p Hope to have it ready by spring. Ahrma has a big event in Ocala area this Feb, CHECK IT OUT! better yet show up with your bike and ride. Great people and loads fo fun! I can get you a number or just visit there web site.