1968 NOS gas cap: What is a fair price?

Yeah I think the other clue is that the original part was a C7ZA (not C72A) which means the part originated from chassis engineering division. Whereas the C8ZZ originated from Ford parts and service Division meaning it was a service replacement part.
C- the decade
7- the year the part originated
Z- the car line (mustang)
A- Chassis Engineering , or Z- Ford parts and service division

my box doesn't have 1986 on it , it has 1966

Okay my bad! My 50 year old eyes saw 1986, but you are correct it is 1966. Mechanicalguy48 explained it better than anyone. That is why I love this website the knowledge is amazing!!!

Cheers,

Ron

so then mine is a 60's service replacement cap, not one of the assembly line?
how would this affect a concourse car???

In some cases they accept the service replacement parts and in some cases they dont. You would have to talk to an MCA judge on that one I think. Personally I have never seen them take off a gas cap and look , I think they go by external looks, but it depends on the class too. In trailered concours they are a bit more fussy then say in driven concours class.

I have been to four MCA concour trailered shows and I have let to see a judge remove the gas cap.