Your wheel cover is for a '67-9 Barracuda and should be for a 14" wheel. Measure across where it attaches to the rim....should be a little under 14 inches there.
I measured it at 15 3/8" and when placed against my 14" rim the overlap the rim of the wheel and it does not line up with the air valve. They are definitely for a 15" rim. Keep trying fellas!!!