My 66 GT Fastback is currently undergoing restoration. Today, I decided to clean up the two front spindles, blast them and paint them. The right side has a casting code of C3DA-6017B, correct for 1966 cars. The left side has a casting code of C3DA-6018B, correct for 64.5 - 65 cars, with dates prior to 9/10/64. It should be C5ZA-3108-B for both later 65's and all 66's. Hmmm...I guess the spindle broke sometime, and it was replaced with an early version. The part numbers are C5ZZ-3106-C (installed), but should be -D. I wonder what the changes might incur with the various parts installed on the spindle...anyone know?