'69 A body head rests

I asked the same question to a vendor at a show last summer. The answer I got was, and I may have this backwards (check into it) The chrome "pegs" that go into the seat, one in longer on a Bucket seat, a bench seat has both "pegs" the same length. Again, I could have this backwards, bench -bucket but that was the difference. Make no sense to me why it would matter...but... If someone else has more info on this I would like to hear it as well :)