ruppster,
i think the cranks are ok for sub 10k rpm motors, they just need to be balanced and trued with good bearings installed. you know how your motor starts off smooth and gradually gets more vibration until you feel like the motor will come apart. it will! with a balanced crank the motor feels a lot like my panhead, there is a definite low rpm vibration, and as engine speeds increase, the motor gets smooth as butter.
i am designing and building my own pipes out of .023 stainless. my chambers weigh less than the stock pipes. my last pipe had a longer baffle cone for more over revs and it was letting me hit rpms slightly above 11k, which ate up some big end bearings. my next pipe will have a shorter baffle cone which will give me a higher peak power and act like a rev limiter, hopefully somewhere around 9500rpm. the only driveline failures i've had were with a bicycle chain as a drive chain. not only did it break, but it caused all kinds of vibrations.