I hear you, i had a TGB laser Taiwan made with gy6 variant, i swapped that motor into agy6 China bike and the motor subframe was slightly different. I just had to grind one side off and shim the other side. There's differences for sure, not many tho. Every variator component will interchange with GY6, EVERY top end (cylinder kits, heads, cams, etc) will fit. Final drive like you said is different, same with stator. The angle of the exhaust flange is different, but a GY6 head will fit a Kymco gy6 based motor. I would never switch to a gy6 based on parts availability, your can adapt darn near any performance part from gy6 to Kymco. Some other slight differences I've found, if you put a high lift cam in, you will need to switch to gy6 rocker assembly. Any gy6 performance intake manifold will work, same with carburetor upgrades. The kymco made parts are 10x higher quality than China GY6.