I'm working with a 67 390 GT motor from Dearborn and I removed the non factory blank spacer from the passenger side exhaust manifold to install a factory exhaust control valve and found the valve doesn't fit against the manifold. So a look at the number on the manifold read C7OE-C which has a larger boss at the base of the stud where the valve meets the manifold, and the reason why it wont work. Was there a change over from the C6 manifold during 67 and I may have the right manifold and the wrong valve ? The car has a build date of April 28 1967 and the engine has early April dates.