Ok had to narrow our search here..looking for some good condition factory original rear leaf springs from a 66 fastback with GT package...this is what I have been told
Rears are marked (bottom leaf) C4ZA 5556 S
and the date code: for example: 16 6E or 16 E6
which means day 16, 1966. E probably stands for Eaton,
the manufacturer, but I am not 100% sure.
email me please at
Jimmy