For the front brass distribution block (2B257):
For drum brakes there was a early (very early, pretty early, pick your poison) version C7ZZ-2B257-A, and then the rest of the model year C7ZZ-2B257-B. I don't recall reading anything about this running change.
The disc brake distribution block is different than the drum - service part number C7ZZ-2B257-D.
The actual switch is a one year only part used on all Ford (did not check L-M) 1967 models, C7AZ-2B264-A