Hi,
for my application (1967 390 GT, November 66 San Jose), the correct speedometer cable part number is C7ZZ-17260-J.
I have two NOS speedometer cables and one is gray, a common service part, I suppose.
The other cable has a black housing and a tag with the identification number C7ZF-17260-A, which corresponds to service part number C7ZZ-17260-J.
Is the black one an early replacement part or a factory part?
Laurent