ok, back from playing in the garage...

the two green machines I have are actually Xenoah, the two minutes I spent looking on google/ebay says they made a decent amount of snowmobile engines, but didn't dig all that far... the plugs stick straight out the jug instead of at an angle, twin pinned ring domed piston, same or different model of similar carb as the stihl and toro engines, points ignition, counterweight on both sides of the rod, cast iron or steel connecting rod (floating needle bearings),

the one you have looks like the Stihl trimmer I have though so they're probably made by Mitsubishi...