[DF19638]

Those are generic 66 model year FE heads. The only difference is that those got the diagonal exhaust bolt pattern for use in the unibody cars. That would be the Fairlane and Comet only for 1966. For 1967, when the Mustang got the big block option and the Cougar was added, they all used the C7AE-A heads. For 1968 they all got the C8AE-H except for newly added 428CJ which got the C8OE-N heads.