*EDIT* Found it!

The shop manager is re-covering these seats for someone to put in their hot rod. He doesn’t know what they came from but between the plastic on the back, the electric plug underneath, and the blue-black vinyl I’m guessing it can’t be newer than late 60s. I’m getting a 70s American vibe, and it must have been a 2 door because of the latch on the side and the way they fold. The backboards look very 70s GM but I’m not sure.

*EDIT*

They’re from a Mustang II Mach I

Image from TTAC

The Truth About Cars had a “junkyard find,” about this car.