Kiekhafer/Mercury years ago made some air cooled two stroke engines. Yours looks like one of them to me. I had a home-made rotary lawn mower with one on it. The perfectly round cylinder and the (missing) cast blower housing were almost trade marks of the Mercury 2s engines.

The air cooled Mercurys were mostly government surplus, used in WW 2 as auxilliary power units in many applications.

Yours could well be built by a later company copying the original Mercury design. They weren't bad engines, but often hard to start.

You are missing the flywheel and the blower housing, if you can find ones to fit it shouldn't be too hard to get it running again, but I really don't think it would be worth the effort.

Bill.