 The H6 engine (6 cylinder horizontally opposed "FLAT") built by "Air  Cooled Motor company" is very similar to engines used on Porsche  911s, some Subarus and many civilian aircraft to this day. It had  overhead valves (pushrods) and was converted to be water cooled. It  was 335ci displacement 5470 (slightly smaller then a "Small Block"  Chevy V8) and had 166bhp with 372lbs of Torque.