1968 2dr sedan

I don't have a sedan, I took mine out in the early nineties and returned them last year. I tagged them but something ate the tags. I put them all on the floor side by side and lined up the centers. Most roofs are narrow at the front and wider and taller as you go to the rear. So line them up shortest first, longest last, while the ones that are same length should gradually have taller side curves as you go back. Put them in the holders and see if they match the roofline. Go on EBAY and buy some extra clips to hold the headliner in, the factory guys were good and could do it with a few on each side, I needed about 2 times as many or more.
Good luck