I found the 'flywheels' for this in my parts box... not sure what they were originally. Casters for tank treads, perhaps? Anyway, I used them in this scratchbuilt farm engine. Other than the flywheels and resin bolt heads (From Ma's, of course), it's totally make up from scraps of plastruct and pvc tubing.
It doesn't represent any specific manufacturer or model, it's just a generic, horizontal hopper-cooled gas engine.