Hey Brett,
It is a very long time since I worked on 35mm projectors.
Difficult to ascertain the size from your pictures.
But it is missing the lamp house, unless there is a candle light holder hidden in the back of it?
(Our dias projector was run using two carbon rods for light for projection…)
My gut feeling is that you might want to look at old Film FX production, back in the days when there would be a projection on the background, or films would be merged later.
Nevertheless, would love to hear your findings when you do find out.
Atb
Mads