The way I read the rules for Production is even more restrictive than SCTA or ECTA. Chapter 4 states:
Production class motorcycles shall not be modified from Original Equipment at time of manufacture. e.g., frame, forks, gas and oil tanks, seat, front and rear lighting, fenders, wheels, brakes, air intake box and (unmodified) exhaust system. They shall also contain the engine that they where originally produced with.