67/68/69 bucket seat differences

So 1968 seats had holes for the head rests?
Yes, and latches for seat backs. Before 67 the top member of the seat back frame was round tubing. When they changed it to square ( and punched holes for head rests ) it got about 1/2 inch shorter. They did tend to use up existing stock but majority of 67 seat backs will have the later design.