Hey fatcharlie. Are you thinking of converting a trimmer or blower engine and saving weight by removing the flywheel? Or getting an electronic ignition plane engine and run it on glow?
I wouldn't want to convert an EI plane engine to gas glow except to experiment. For a trimmer engine, you want something compact, light, easy to trim (grind, hacksaw), and easy to mount. There are many discussions here about homelite, poulan, etc.. I really like my little Kioritz/Echo 21cc engine. It's not a powerhouse, but it is so small, reliable, and has grunt. It spins anything from an 14x6 to an 18x8 prop and only equates to 1hp, but it pulls a 120" ws, 16 lb oldtimer/floater no problem. I'm guessing the big Mud Duck foamy will be about 10-12 lbs. and you don't want to blow the wings off.