Only 2 others known and 1 of those still runs regularly..
Direct drive, con rod to wheel crank.every time it fires it travels 1 meter IIRC
Flat twin as well
None of this shaft or chain drive malarkey, just connect the conrod directly to a crank on the rear wheel
If the rear wheel is 18" diameter that will do the princely speed of 12.85mph at 240rpm. That will be more than fast enough considering you have to stop the engine to stop the bike