Now, personally, I think these guys are full of crap, because my truck is a '72. Here's what they say:
So here's the link if anybody really wants to go see it. I call shenanigins on them.Ford Trivia: Ford Motor Company was wrapped pretty tight back then. In particular, the system used by Ford to identify parts is a brilliant and easy to figure out method of determining what decade and year your car or the part was made, giving you an advantage in finding what part you want fast.
The C in C-4 stands for the decade of the 1960s. As the letter D would indicate the decade of the 1970s and so forth. The number immediately following the letter designates what year the part was produced. Thus we can conclude that the C-4 was first produced in 1964. C being the decade of the ’60s and # 4 being the year in that decade. Hence C-4, 1964..
http://www.gottransmissions.com/blog/re ... somatic-c4