He's one of the vendors here advertised to the side of this post. I was just looking and I would imagine that the 32cc four stroke Titan at 1 1/2 hsp. would be the ticket. I believe the friction drive mounting kit and the engine are sold separately as there are different engine choices. This would be an easy to start, quiet and reliable engine, something he can count on every time he goes out for a ride. ( No, I don't work for Dax).
It would be good here if someone actually using this setup up or something similar would weigh in and advise. I have little experience with friction drive.