OK Ranger Folk:
Today I got the key housing/shaft out - it did involve removing the steering wheel, but now I know how to do it. What an involved mess, though.
Anyway, the broken part is this thing, called the actuator. What I thought was three pieces:
is just one:
The broken teeth are what was causing the gear connected to the lock cylinder to not engage:
You can see the teeth inside that groove; they rotate with the key.
So I ordered the new actuator at Go Ford in Wheat Ridge ($17); it'll be here Tuesday. The worst part is that all these moving parts have a nice coating of white grease on them and it is very messy!
I guess I could have fixed this without removing the steering wheel and the key housing/shaft, but I wouldn't have been able to figure it out without looking at it up close. Live and learn!