Dan, the Deluxe seats have a grained vinyl outer section with a "Comfort Weave" insert for the centers of the seats. (Kind of looks like a cloth insert from a distance, but is woven vinyl)
And the center section is in a specific patern.
Standard is all vinyl with a heat seamed patern in the center section.

Then the door panles (at least for 67/68) are also quite different with molded arm rests instead of mounted arm rests, again patern and all is different.

Many times they list it on the build sheet as Custom interior. But there is no real reason you couldn't put the deluxe in even if it wasn't ordered that way. 99% of the people wouldn't pick up on thet even with the build sheet displayed with the car!

Good luck - Brett!