[Firebirdjones]

That's not stock. As of early last year, my 72 still had it's original covers, and there was nothing like that underneath. I'd venture to say someone has played with the covers before. Simply because the material on the seats themselves is not original, they have been recovered in the past with some form of cloth (and the plastic backs are missing?), and that looks to be some sort of possible seat warmer underneath or maybe an attempt at covering the original foam and springs that are inside rather than using burlap.

You are correct, orange cloth inserts were available in 72 (mine has it) They call it a Highlander option according to the folks here.