Hey, I own a 1985 Honda Shadow 700 and a 1981 CM 400 C, which I have done some work on, including a brand new crate engine from the Japan manufacture back in 2003. If you have a CM with a smaller engine, someone may have replaced the original engine with a CB engine. These frames are very workable and customizable. I´ve seen v-twins installed on CM frames. Hope that helps.