RE: Car/buggy vs. heli vs. airplane engines
Heli engines have a carb optimized for mid range and generally a shorter crank shaft. The carb might be an annoyance but on the OS 50 and the heli 50 the threaded portion of the crank shaft is 7mm shorter, I doubt you would get a thrust plate, prop, washer and prop nut on the crank shaft. They are made for screwing on a fan and putting the prop nut on.