Just to make it clear, as Jeff pointed out, Deluxe Seat Belts were not part of the Interior Decor (Deluxe) Option. Having Deluxe Seat Belts would also include the Seat Belt Warning Light, mounted in a bracket which mounts to the underside of the dash. Having this light would be a good indication that your car had the Deluxe Seat Belt Option.
Also as Jeff noted, there was only one Red Vinyl used for both Standard and Deluxe Interiors. In addition, only one color Red is listed for the 1967 Seat Belts, and it has a C7ZZ Part Number prefix, so it would not necessarily be the same as the 1966 Red Belts.
And finally, the Shoulder Harness Option required the Deluxe Seat Belt Option ; another good reason that your car had that Option.
Supporting information is attached from the 1967 Color and Upholstery Book, and the May 29, 1967 Salesman's Price Book.
Hope this helps.
Bob