Turns out that this is a 1967 390-4V/410/428 bracket. A friend gave this to me, and he normally deals in Galaxies and Thunderbirds, so is likely a 428 part, which would make it the C6AE-9B290-C. The Mustang 1967 390-4V would have used C6OE-9B290-C. What about the GT500 428 PI engine - which of these would that have used? The 428 PI drawing shows C6AE-9B290-C, but that is geared towards a police car not a Shelby.