Just trying to help out a little,,,,,,The letter "C" is Fords designation for 1960 through 1969
and the letter "D" designates 1970 through 1979, so Most of the valves are for the 1960's era, and a few for the 1970's.
Also, the number right after the first letter designates the Year the part was first put in production.
Then, the 3rd. letter (right after the number) designates the Model of car or truck the part is for.
That's my story, and I'm sticking to it, LOL.

,,,,Hope this helps
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