Josh,
Your 68 appears to be a hardtop car, unlike mine with is a coupe or post car. Being a hardtop you should have the decor package giving the car the deluxe interior package. Mine is a very basic Road Runner without the decor package and having the standard interior. The code on the fender tag or at least what you have for the rear seat should give you an idea as to the interior for your car. I'm fairly certain the seats are the same size although the head rest configuration may be different between 68 and 70. I think for 68 you could option out either left or right or both. In 70 I'm not sure what you could order. Mine has no head rest at all...whiplash special...

Jim