You should sell the 68 seats and just get the 67s. If you 68 seats have headrests, then you can get enough for the for the seats and new covers.
John L. Anschutz
Allen, TX
68 Diamond Blue Coupe - 302
68 Acapulco Blue Coupe - I6 - 200
http://www.dallas.net/~jjmsansc/parts/Stangs.jpg