In case anyone is interested, I've been able to identify the engine....
It's from Czechoslovakia. A 1950's vintage ITES engine. Very rare. A couple videos on YouTube of a slide valve version, but none of the oscillating model like mine. Since mine also lacks a sight glass I assume it is a earlier or cheaper model. The ITES brand is somehow related to IGRA, another brand from Prague.
Besides these horizontal engines, I've discovered ITES made at least one vertical boiler and at least one overtop model.
Surprisingly, while ITES engines are rare they don't bring much at the auctions I've found, on the order of 75 British pounds (how do I key in a pound sign?). So relieved of the guilt of bastardizing a historical piece, when I get around to it I'm going to do a restore/upgrade using commercially available parts (e.g. Wilesco, Jensen, or Weeden) and create or adapt a new chimney.
Attached is a picture of a new, slide valve ITES along with accessories.
Paul