Richard : Here we go again ; another MPC "conflict". You apparently looked up under the "Hood" Section (Section 16606), and I looked up under the "Emblem" Section (40282).
Both the 1967 "Only" and 1960-68 MPC's show C7AZ-16606-A, B, C and D for the Hood Letters, and C40Z-40282-A, B, C and D also for the Hood letters ??
I guess the only way to tell for sure is to check the numbers cast into the back of the letters. Unfortunately, my originals are with my 67 in Colorado, so I can't help with that right now.
In checking the Body Assembly Manuals of both 1966 and 1967, the 1966 shows a "C5" Identification Number, while the 1967 shows a "C7" Identification Number. This seems to support the C7AZ letters for the 1967 Hood. However, the 1967 Body Assembly Drawing id dated 2/27/67. This made me think that there may have been a change before that date. I then checked my November 1, 1966 List Price Book, and the C7AZ letters are listed there. Thus, if a change did take place, it had to be before November 1, 1966. So, at this point, I would say the only way to know for sure is to check the Identification Numbers on very early Models, to see if they are "C4" or "C7".
So, Brian, in your case, I would be on the safe side and say the letters you have are for 1965-66, unless someone can verify that very early 67's used the "C4's".
Just another one of those "easy" look-up items that turns out not so easy.
Bob