I did not recognize it when you posted the images a couple of days ago.
Looks to all be fabricated rather than using castings so could be totally free lance or could have been based on the mechanical layout of something else that was available cast. I can't think of a drawing for a barstock engine that it would be.
Is there an inlet valve on the end of the head? I can only see the exhaust. Plugged hole on top of head may have been for a spark plug. Holes at side look more like they could have taken a hot tube and chimney support.
Not sure about the hole in the side of the copper water jacket as it does not look like it ever had a pipe stub soldered to it so, assume there is a water inlet at the bottom of the jacket?