i guess the point is... if you want to ride hard and go fast .... expect to do a lot of corrective work before even putting the motor on a bike, you need better needle bearings, a titainium wrist pin to lighten the top end, cut piston skirt and dome ramps,port an polish, port match, free flowing exhaust, 16mm carb, higher compression 10:1 is a good comp ratio to shoot for as it offer performance with out too much stress on the motor... all this will lighten the top end reduce vibrations and allow for higher rpm's safely.
a motor like this will last a long time with proper riding and matenance, and will be more powerfull and fun to ride than a stocker...
now if your not into doing work like this and just want to slap it on and go... be aware that you at least need to clean up your ports as a single casting flash from a porly made cylinder will destroy a brand new motor on the first rev!!!!
after cleaning the ports make shure the intake and exhaust are matched as good as you can and the clutch is adjusted right, check the head to see if its torqued right, and you should be good to go ! if you maintain proper lubrication and ride it easy to normal, it should last at least 5,000 miles !!! remember to keep it under 7,000 rpms or the vibes will destroy the motor real quick and where it out faster, but all in all with some minor corrections like cleaning up the ports, matching the intake and exhaust and retorqueing all the bolts a stock china girl should last a long time !!!
all this being said.... i still wish they had a cast iron cylinder !