I've done this before with other bikes as long as you get a good quality high heat paint you can spray it in the frame and the paint will cure as you run it.Plasticoat is about the best I've used but Rustoleum will work.Just make sure it's rated at 1200 degree or better, I know you motor won't get that hot but the other stuff they sell at kragen that's only rated at 350 is crap.Make sure the motor is spotless, clean it with something that will cut grease like rubbing alchohol,acetone or brake and parts cleaner and make sure you get all of that off or dry before you start.