So what's this then?
Air-cooled aircraft(?) radial, cylinder, head & piston.
My first thought was a Wright R-975 (as also used in the Sherman tank) because the exhaust side is so much more heavily finned than the inlet. However it looks wrong for that. Could it be a Kinner?
I think we can agree on the "UNKNOWN MAKE POSSIBLE ROLLS ROYCE. " part though 8-)