What do motorcycles have in common with airplanes? The answer is easy - Henderson engines. There have been a number of wackos who decided to adapt Henderson engines to power their airplanes - primarily the DeLuxe engine. There were only a few major modifications required. First was to cut off the useless transmission, and provide a propellor drive. The exhaust system, carburation, and other goodies then needed to be modified since the back of the engine was now the front. A larger oil pan was needed, since an airplane assumes angles that a motorcycle never could. Each builder did these in their own unique way, as well as many other smaller modifications.
There were a number of builders who modified Henderson engines for aircraft work.