I don't find seat foam available for bench seats, but the Year One offerings for buckets seats says '73-76. So I would guess the bench seat is a match as well? But no idea beyond that.
I would add that the high back bench seat uses bucket seat foam for the backs, adding to the idea that the seat is the same. Edit - this is a flat out assumption on my part. The latch is different between a bucket and bench seat so ???
Also, pretty sure the difference between years for seats is more about the shape of the foam and the way the cover was stitched (design). I don't think the structure really changed much through the years, it was more about the foam and covers.