Pretty sure a cb250 engine bolts right in and you'd get leccy start too. The twin carb xr250s were a great bike in the day, and there's still plenty getting around today, they outsold all the other 4 stroke 250s combined.Get some pics up once you get started, I'm currently building a Honda engined BSA rigid bobber and have a 47 CZ rigid frame and a dt175 engine waiting to be married together