This is a bracket change that occurred during the ’66 model year. On the right is the early bracket with a dimple reference point; the dimple goes into the alignment hole on the Mustang’s core support. On the left is a revised reference tab bracket that showed up later in the ’66 model year. To the best of our knowledge, all ’65 Mustangs had the dimple bracket. We’d like to hear from anyone with proof to the contrary to see if we can establish a pattern across assembly plants.