I have a good friend with a couple of their marine version in his boats. He also has that version in a 5th scale rc. They are cool, but the amount of RPM they need to make power, makes them kind of useless on a bicycle. There really isn't much usable torque.
Does your friend's engine have a 76mm centrifugal clutch?
If it does, and has the standard 4-bolt bellhousing, it will bolt onto any drivetrain used by contemporary engines, such as Stxxxn, GEBE, 3:1 and 5:1 goped/pocket bike engines.
High-rpm r/c engines CAN be tamed and harnessed to bicycles. I ran a few 4.5hp CY460 engines on my motorized bicycles. They had excellent roadside manners @ any speed @ idling,low/middle/high speed. The key is the 76mm clutch & bellhousing, silencing the exhaust and throttle connection. When geared properly, r/c engines are as docile as any other motor bicycle engine. When suited to an SBP China Girl high performance exhaust, the 460 engine becomes VERY quiet @ any rpm. I swear I could hear the piston ring acraping the cylinder @ idle speed. At high rpm, it reminded me of late-model crotch rocket engines. You can hear the pocket bike transmission over the exhaust.
Anyone know the optimum torque & hp rpm range of this engine?