I apologize, and should have been more specific. I meant that AFAIK, no Mustang ever got a dual-quad 427 from the factory, and that a street-use OHV 427 probably couldn't effectively use a dual-quad.
[edit]In '67, the Fairlane got a dual-quad 427, rated at 425hp and 480 ft-lbs, with 11.1:1 compression. In '66, the same engine was offered in the full-size cars only as a race option.[/edit]