Yeah, I went and looked at a picture of my 66-1, and realized I remembered wrong about the slide plate over the bobbin...horizontal or vertical, the slide plates look almost the same on the older machines.
Anyway....I still think a 1940's era with the Godzilla finish. Don't understand the lack of a motor boss, either. Maybe an aberation? Some of these old gals keep their ages a deep dark secret!! :-)