Tom Boice has worked for a number of years with the old O.S. .60 open rocker four stroke glow engine converted to spark ignition for SAM Texaco events. A number of mods to get 33 minute motor runs on 28 cc of fuel. Special fuel tank as seen in photo. Head shim to decrease compression for gasoline fuel. Remote O.S. .20 four stroke glow engine carb used (see photo below). Special fuel formula and probably other mods I am not aware of. I can verify the 33 minute motor runs as Tom let me fly his 1600 sq. in. Bomber in Texaco last year at 3 SAM contests in the Mid-West. Three contests and three 1st place in Texaco with Tom's big Bomber.
At the last of these three SAM contests at Fort Wayne, Indiana Chuck Hutton offered me his old O.S. .60 open rocker four stroke glow converted to spark for Texaco. I accepted Chuck's offer and he mailed it to me after the contest. I cleaned it up and sent it to Tom with two spark plugs and two ignition modules. Spark plugs may not be the brand that Tom uses. Tom said it looked new until he checked it out and could see it had been run a lot with carbon on exhaust valve. Tom said it is a very good engine and he did his mods and gets 33 minutes with a 18/10 prop turning 2,500 RPM. With that prop that is all the RPM you need for a regular size Bomber.