Maynard Hill, holder of many model records (also the group that attempted to fly the Atlantic) used a regular O.S. .52 4cycle for his duration record airplanes in the early-mid 1980s (current record is 33+ hours, set in 1992 by Mr. Hill and friends ). These had been converted to burn Gas/Oil using a standard flywheel type ignition system (these engines turned at low RPM with big props 16"-18" I think). As far as I know, the only modifications he made to the engine, other than ignition type, was to replace the original push-rods with a harder material (some said it was just drill rod).

I have a Picco .40 2 cycle, converted to burn gas/oil that has run continuously for 40 hours on 100/1 regular 2cycle Aimsoil, 14x6@6000, no heating or lube problems.