Let's get back on topic.
A motorcycle is obviously a two wheeled vehicle and a car is a four wheeled vehicle. We can argue about sidecars and tricycles till the cows come home. IMHO, the difference is that a sidecar has one driven wheel and a tricycle has two.
IM<HO that the engine makes absolutely no difference. Aircraft engines have been used in hydros; they're still hydros. Aircraft engines have been used in LSR 4-wheeled vehicles; were these cars, airplanes, or hydroplanes?
BUB made a from-scratch engine and put it in a two-wheeled LSR; this is a motorcycle. Anyone can make a modified engine from any source or from-scratch engine and put in in any LSR. If we place a Hayabusa engine in a go-kart, it's a go-kart. Don't worry about the "source" of the engine, it's the vehicle it's in and the class that it fits into that matters.