Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

No doubt in my mind that Uncle Cletus is to blame for this one.
Definitely looks to me like they just removed the sightglass, drilled the lower gauge-hole up to fit the heater, and added another to fit the overflow plug instead.

...but still in most aspects an amazing engine, and definitely no less interesting with the unshielded electric suicide setup.