[Joeaksa]

Continental and Lycoming were making both radial and horiz opposed air cooled engines long before Porsche was in business.

That said, the engines are very much alike in many ways and it would not be a stretch to assume that the old man had seen a horiz opposed aircraft engine and decided to incorporate it or its ideas into his cars.

The early radial engines were very different in that the entire engine assy turned, not just the crankshaft and the prop was bolted to the engine. Later ones were changed where the engine was bolted to the airframe and only the crankshaft moved the prop. This style of engine was used up until the last prop/piston fighters then started to lose favour to the jet engines.