Note that the MPC calls out your 9773216 seal AND another, different size seal 9784286 also used on some 64-65 Tempests (and GTOs) as well as full size 66 Pontiacs. That crosses to SKF 19273. Specs here:
https://www.rockauto.com/en/moreinfo...835254&jsn=265
Maybe this seal is needed????