Are these stock seats for my 1971 Blazer?

[hahnn6]

Hey all,
I just purchased a 71 K5 that is very original and unmolested. (still has the AM radio in it, complete AC setup, and original drivetrain). But I noticed that these front seats seem fatter, and the back cover (it's metal) is larger than what I see online. I've some Blazers online that have these seats, but what are they out of? Is it just a different upholstry and padding job that changed the look of them? Still doesn't explain the backing to me... Thank you!
Nate