It's amazing the little stuff you forget on a big project. Thanks to @latemodel_resto we could fill in the blanks.
These ’81-’88 Mustang Convertible & T-top Rear Of Door Run Channel Seals (PN A40-07-1; $44.99) were the missing link on Fox 500's door.One day I realized there was something missing on Fox 500's doors. After addressing lots of other areas, this became pretty obvious.
These really should be installed before the door trim and door panel. I'll fasten them permanently with rivets when I pull the door panels back off for the stereo. For now I just pushed them into place.
That's much better. Now the door has that finished look, and water won't just rushing into the door.