Re: oh the possibilites...
Each to his own but if you choose the Chinese frame mount, IMO you're missing opportunity. I have a full suspension bike with a rack mounted Chung Yang R460 engine. It is a quality motor made in Taiwan, 46cc, 4.2 HP @11,000 RPM. It uses a Walbro fully adjustable pulse carburetor with a totally sealed fuel system, very reliable. The engine turns a pocket bike CVT transmission and is routed to a freewheel sprocket.
The point being, there is a world of possibilities with the China Girl style bike engine at the bottom, IMO.