i disagree.
first off, to street bike standards, your motor there is the laughing stock of all bike engines. its design sucks, its HP output is on par with much smaller motors, and it is much heavier than others in the same class.
second, street bike motors are built with the frame in mind and require support in certian areas. streetbikes use their motor mounts and frame to give stability to the motor. by taking that away and putting it into an off road frame, you are adding new stress and vibrations to the motor that it wasnt designed to handle. remember, that motor was designed for road use. there are much fewer bumbs and vibration on the road.
thrid. believe it or not, that 600cc motor is designed with a MUCH tighter tolerance than any off road engine ever will be. it is designed to give the maximum amount of HP it can possibly give. to do so, the engineerss take into account that the reduced vibration of street riding can also result in thinner lighter parts. street motors are designed not only for power, but are also designed to be as light as they can possibly be.
how can you expect smething designed in this manner to hold up to off road riding?
theres a reason that your stock off road parts are thicker and heavier grades of metal. maybe you just figured it out the hard way.