Right. In the old days, even fairly small engines used spark ignition. My uncle, who held several model boat records and built his own engines, had a supply of miniature spark plugs from Germany during the '30s -- which, of course, dried up.
But I remember seeing those tiny engines in airplanes during the '50s. The spark coil was almost as big as the engine, and resided in the fuselage around where the cockpit would be.
Before glow plugs, the alternative was compression ignition -- pseudo diesels. Of course, they're still around.