Re: Suggestions on engine to get?
Get the Dax or MBR motor.
It has a 40mm 'ballanced' crank.
the others have a 38mm crank that could be 'rough as guts'.
The longer stroke Will give you better pulling power.
The 'balanced crank will let it rev further and smoother.
The Ebay motors I have bought have required total strip and rebuild including the replacement of dodgy parts, then still be burdened with inferior parts.
You get what you pay for.
Unless you have fabrication skills, stick to the 'China Girl' you get everything you need in the kit and it can be installed in a few hours.