Marti's Mustang By the Numbers has trim codes 2F and 6F for Raven Black. Of all the Raven Blacks (10,526 of 427,207), there were 280 2F's and 65 6F's. Code 2x were standard buckets, and 6x were decor buckets. So about 3% of Raven Blacks had saddle interiors, and about 0.06 of all 67 Mustangs.
I'd love to see pictures of this combination: might be really sharp!