Seat base, whats it fit?

I have a pair of these seat bases but not sure what they fit.

They were in our barn with some mid teens Cadillac parts but could be something else. They tilt in one direction but not to 90 degree position adn it looks like they swivel too under the rust with a detented notch on the swivel.

Thought they may be for some kind of jump seat in back of a touring car. Any ideas??