people have done it in 1/5 scales. overall, its disapointing. industrial engines are designed to run at a lower rpm and put out way less power than an engine designed for r/c (or go-peds), such as the zenoah and cy 23-30.5cc engines.
i think most of the people who have done them have been trying to save money putting together a cheap 1/5 scale they have bought. the end result is by the time you figure out how to mount it, get a clutch figured out and make everything work, you can buy an r/c engine. the cy 23cc goes for around $150 brand new, used ones can be had for $100.