The engine with 2 spark plugs is an RC airplane engine. 48cc, 8,000 RPM 4.2 HP. The problem with this engine is that it does'nt have a pull start, and you would need to reduce the RPM, and no centrifugal clutch. I think it's too much work. But it would really look cool on bicycle, like a BMW motorbike.
I think it would be easier to mount the engine I posted in the link, with more HP, and less work.