The engines in the Linhai maxi Scooters are indeed Yamaha clones. Unfortunately, I just don't know enough about the Yamaha scooter engine families to help you. I have seen a Linhai 400 (around 370cc) for sale on some Chinese scooter vendor sites, but they cost a lot more than the 260.
Here is a pic of a Linhai VOG 300 engine/cvt from scrappydog. See if it resembles your Yami engine.
