Those I believe are 66 castings with smog port bosses cast into them, not machined on the one shown. Neat find but not at that price.
My June `65 built Nailheads have these "603-E" heads with the smog port bosses. My `66 cars also have smog port heads but the casting number ends in "603" Tom Mooney
My guess is these heads were manufactured for Gray Marine Corp and intended for the 401 marine engines Tom Mooney