V Twin model engine

I'll bet it's Italian... maybe off of a motor bicycle. (because of the sprocket on the output shaft)

Its small, less than 4" tall

Looking thoroughly at the pictures, I think it's not an engine at all but should look like one.

1. The output shaft with sprocket is not in the centre
2. The bevel gear driven thing with 2 wires coming off is not a magneto or a distributor with points. Could be a HT distributor only but there is no 3rd wire
3. The aluminium tubes for the rocker arms end up in the circular mounting ring for the pseudo rocker covers
4. The holes for spark plugs are machined in the cooling fins and not in the cylinder
5. I can't see a carb. only an air intake.

Looks like a modified air compressor to me.

Looks like it may be a hummingbird engine. They run on compressed air etc. The (what appears to be intake ports) exhaust ports at the bottom of the cyl release pressure. When the piston reaches TDC valves allow pressure in pushing the cyl which pushes the piston down. When piston hits BDC the exhaust pots are open. To relieve unused pressure. Fly wheel momentum brings piston back to TDC valves open, stored pressure pushes piston down etc repeat. Many variations and applications including model airplanes.