That is the ultra-rare 1970 Styled Steel wheel. It's even the correct color. The wheel is the 1970 14x7 SSW, the cap is the same as the 68-69 cap, and the ring is also the 1970 SSW ring. The ring was used later on Granada magnums.
I have very rarely seen these wheels, even though I've been into Mustangs since before 1970, and I have never seen them on a Grandé, which the photo car is.