I searched and got some really good information but there are a few clarifications that I would like to ask for.

When set to blow out of the dash vents at me, my A/C blows out of the dash vents as well as out of the windshield vent.

I looked around the gas pedal (well, diesel pedal) and found the motor that controls the doors. One of the levers was disconnected. I reconnected it (I had to get some long nose pliers in there to carefully press it into place), so now when I change the a/c mode the motor moves both levers. However, the A/C still blows out of the windshield vent, and from what I can tell, with no change in intensity.

I am thinking my next step is I am going to have to "really get in there". With the actuator motor in place, there is no room to wiggle or tweak anything, so I assume my 1st step is to remove the actuator.

Is there a documented procedure on what to do next - how to get to the door that controls the windshield vent flow? I am assuming that there is some sort of a door that is not functioning?

if you have kids then the most likely cause is debris falling down the defroster and jamming the door.
I have seen many a quarter/lolipop stick get caught under the defrost door and jamb it in 1 position.
In the 80's we used to get a hole saw and drill into the heater box(careful not to hit the heater core or evaporator) and try to fish out the offending debris with a piece of wire and just silicone the piece that the saw cut out back in place.
best way to fix it if thats really your problem though is to remove the dash and hvac system and take it apart.
its a great opotunity to replace the heater core for piece of mind.but its a very BIG job.

When you say BIG do you mean the whole dash removal?

Is the defrost door controlled by one of those levers? The lever is attached to a handle that, I think, moves the defrost door, and it DOES move. The handle is kind of sticking out at a strange angle though; I am going to have to take pictures to explain this better...

yes the levers do move the doors so if the exposed shaft moves then maybe you reinstalled the lever backwards?

The rubber seals on the edges of the doors will fall apart over time. Have you seen black rubber stuff falling out of the heater vent? When this happens the damper doors cannot seal all the way, causing leaking. Mostly blowing extra air out of the defrost and heater vents. No way to repair without removing the whole box....One of my trucks suffers from this. I have an extra box with good damper doors, but I am to lazy to rip the dash out. I made a cover for the defrost vent and block the heater vent in the summer. Works....

First thing I am going to try is unbolt the motor... maybe then I can at least get my hand in there to play with the knob that controls the door....

Mine just takes its sweet time switching over. If its set on high it may never switch, so i have to turn it on low. 30 seconds later you hear a thump as the flapper finally switchs positions. I think the actuator is the problem in my case, but i dont know about yours. Does sound like something might be stuck in there.

Well, I got the stepping motor out, and what it looks like is the handle that, I presume, controls the defrost door, is just loose in there. It is bent, and I can slide it in and out, and the other end of it does not seem to be attached to anything.

It appears that the Chilton book does not cover the air box removal...