Ten years before the VW bus was conceived, White was a building a delivery van with a rear aircooled boxer four, built by Franklin, and based on one of their aircraft engines. But no swing axles. For that matter, I’m not quite sure how that rear suspension works, as it looks like there’s no room for a drive shaft. Is it all one rigid unit with a pivot in front for the engine?
That’s what it looks like, from this picture, the best I could find, of the drive train. Looks like a rigid unit from engine, transmission and rear axle. So there must be a pivot or some sort of flexible mount at the front of the engine.