Re: So I heard about this Death Race...
Welcome to the place.
There are no "best engines" as far as that goes. The QC at the chinese factories is appalling at best, so these are hobby engines. They can be raced, modified, tweaked, or just maintained and ridden daily. They are what you make them.
As for the bike choices? Endless. Almost any diamond frame and most cruiser frames will work. Have a look around this site for ideas, and no-no's.