Which one(s) of these Is an original big block OEM exhaust manifold for the driver's side?
They all are. The top one is the 017 M-Code 440 manifold, can't tell which year the middle picture is due to the angle but it is a 383 A-Body manifold, the bottom one is the 729 68-69 383 manifold.
Middle one appears to not have the #3 pipe indent so that would make it the 67 ?
