Did they stay the same? In a word, no. From the 60-68 MPC I'm counting six different part numbers. Refer to the attached pictures that cover through 1977
What is interesting to me is the 1967 289 HiPo (including GT350 I presume) starting the year with C6ZZ-A and on 11/1/66 moving to the C7ZZ-C like the C and A code. The MPC does have its flaws, but I'm wondering if anyone has noticed this change.
C5ZZ-6A023-A
C6ZZ-6A023-A
C7ZZ-6A023-A
C7ZZ-6A023-B
C7ZZ-6A023-C
C7ZZ-6A023-D