Well, nothing's ever easy. For some reason, the left-hand threaded hole did not want to take an M6-1 screw. All the others were. Naturally I tried to force an M6-1 bolt in there and snapped off the bolt head. Broke off some drill bits trying to drill it out. Ended up using an air chisel to chisel off the protruding stud, and then finally drilled it out. Then it was too big for an M6, so I tapped it for a 1/4-20. I bought an M6-1 tap and chased the rest of the threads.
The reason they knee panel was loose was thanks to the plastic stakes that held the spring retainers breaking.

So, on tonight's episode of Fixing Snap-Together Fords, I epoxied the spring retainers back in place:
Both screws were previously missing, so it was basically hanging on by a single snap post.
Now it is firmly back in place.
But, while sitting on the door sill while working on all of this, my fat butt broke off the side trim.
Fix one thing, break something else...