Re: Suggestions on engine to get?
The 66cc engines that Dax sells on his site are of nice quality and they can handle a few extra horses if you decide to upgrade, but these are the only "China Girl" type engines I'll buy for my bikes.
Now if you want an engine that'll really rock, he also sells a 50cc KTM clone engine that puts out 9Hp in stock trim.
Another option is to buy an engine from MotorBicycleRacing as his engines are of the same quality as the Dax engines and they have been proven to withstand at least 10hp in modified condition, he also sells a 9.5Hp version of this engine for racing bikes as well as lots of really well designed and built performance parts so you could build a beast of an engine if you already have a good stock engine.
Another option is the DeNardis engines sold at denardisengines.com, they are the ones who continued to build the Morini engines after Morini quit building them