There is a local guy on CL that has a Yamaha FZ400 chassis with title but no engine for reasionable that gave me pause thinking about a swap like that. That said it is set up SuMo now so is 'sort of not really' the same thing. ; )
Am doing road racing this year so may consider using the KX5 next year if I keep it. Might do a track day later this year to see how it goes.