'68 Barracuda is A-body. However, the seats you have pictured are not original '68 Barracuda seats.
If you're looking for seats for a '74 Duster, you will need '74 and later (IIRC, someone will correct me if the year isn't quite right) seat tracks since the floor pan contours changed that year to accommodate a catalytic convertor, and the tracks changed accordingly.
75 and 6. 74 still had the older floor pan so direct bolt in. On 75 and 6 only one out the set of four tracks on the driver side changed to accommodate the bump in the floor made for the new for 1975 catalytic converter