Morning Michael,
Link for aforesaid machine below:
Yamaha-SR400-cafe-racerQuite "Why?" you would add weight to a "cafe racer" by fitting a one into two exhaust system, with crappy absorbtion "silencers", and pseudo throw over saddlebags, I'm not sure?
As for the "Performance Damper", to prevent torque flex in the frame, when using all that raw power .........?

Apart from that it's neigh bad!
Good health, Bill