I understand that the xtreme motors and the rest of the china motors run different bolt patterns. The xtreme runs a tall cylinder, like the one you show, but has a honda bolt pattern. The rest of the china stuff (lifan, zongshen, gpx, jialing) run a similiar cylinder, but with a slightly wider stud pattern.
One cylinder I KNOW works is the Honda Nice. You can get them overseas quite readily.
I have an xtreme 131 motor sitting in a dirtbike at my mom's in PA. Great running motor for cheap.