Re: engine question
If you want to adapt an engine from another source there is a lot of good information here in our DIY, (do it yourself, non kit section). Weedeaters, backpack leaf blowers, snowblowers trimmers and lawnmowers all have engines, both 2 and 4 stroke that can be adapted to a bicycle. All it takes is some ingenuity, metal working skills and a few dollars. Good luck, keep us posted on your progress.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"