Anyone recognise these buckets?

I have these buckets in my '63 Falcon, but no idea what they came from. Does anyone have a guess what vehicles may have used these? Hard plastic backs, release up high on the side of the backrest, catch in the center of the bottom rear.
Here's a couple pics:




I'm guessing late 60's something with the way they're built, but not sure?

 

Interesting.....I'm curious as well.

 

Mustang II like 74 on...or maybe later Pinto too...

 

Thanks!