i'll say 63-64-65 pontiac, i have a 64 olds and they look the same except for the lines in the seat covers
Definitely '62-'65 GM full size. The A bodies, as well as Corvairs, used the same basic seat but did not have the chrome trim that continues across the top of the seat back.
These are just like the seats in my '62 Poncho. Good frames, comfortable seating too. The ones you are showing are sure worth taking to a good restorer and asking them about a redo on these. Normbc9