Now, I followed through with removing the door latches and going to the bench. Some previous owner had unwisely sprayed white lithium grease inside the latches. This is not a good idea, here's why:
The mechanism is a fine machine with 4 strong springs and delicate movement, made of brass. It doesn't need heavy white lithium, which will only attract and build up dust which will eventually stop movement. What looks like rust, isn't; it's just gunk. Cleaned up, the switch looks new.
rAt this point, you have to reinstall the switch which allows you to easily turn the adjusting screw by hand in order to find the sweet spot that closes the circuit. Hint: the plunger is what you're adjusting; the sweet spot is neither at the top nor the bottom of travel, it's somewhere in the middle. The adjustment can be pleasantly precise. Tighten the locking nut, and it's done.
I did lubricate the whole switch with a spray of Kroil, and then blew it out with the compressor.
Finally, 64 switch looks like those above. Ford entirely redesigned the 65/66 part, giving it a different actuator. They share some springs, but aside from that there is very little resemblance. The build-up of gunk and grease should also be the cause of malfunction on a 65/66, and could be solved with cleaning. (I bought a pair of '65 switches via Ebay for $15, just because I had to see how they worked.) On the 65/66 switch, gone is the tricky plunger, and it's replaced with nothing. The actuator is just a spring which, by appearances, doesn't look like it can be adjusted, and doesn't need to be.
It's great to restore these funky little things. It's American automotive excellence from the artful period. Hope this helps someone else out!
