Just kinda' guessin' Jim, but back in the '50s when Fox was king in the stunt circles Johnny B made the K&B that way because most everyone except george Aldrich flew counter-clockwise. With an inverted K&B and no muffler, the exhaust blew out away from the model and there was less mess on those dope finishes.
That was what some of the old timers of the day told me. Back then I never cared much. On a profile Ring Master, that K&B flooded like crazy and bloodied me lil' ol' fingers, so I wanted an exhaust pointing down. Never occurred to me to put the engine inside the circle. [:-]