Flip top gas cap on a 68 Barracuda

Has anyone put a flip top gas cap on a 68 Barracuda? A friend ordered one for a 69 because he liked the look of the black center but the ring is different and too big for the 68's I see they are listed different in the catalogs. The 69 Barracuda one also fits the 69 and 70 Charger. Are the caps all the same just the trim rings are different? Thanks, tmm