OK. Checking with Chiltons, Haynes and this forum it all comes down to "position the electronic blend door actuator out of the way". Well, I removed the retaining screw and the actuator is still attached to what appears to be a tray which is part of the overall plenum. Even in this forum the instruction given is "remove the electronic blend door actuator". What else is holding it? Does it need to be lifted up? If so, how do you do that without breaking something?

2002, F-350, Lariat, 2wd, 7.3ltr., black, gray interior, antifreeze all over the floor, dead bugs all over the grill.

 

There are two screws on the top of it that hold it down. Remove them, then the whole thing loosens up. You then rotate it 90 degrees one way or the other, cannot remember which direction and it comes off of the T-head on top of the blend door.
Also it's easiest to set the heater temperature to the middle position, (IIRC).
When I did mine last year the hardest part was getting those PITA quick connects disconnected from the engine side because I didn't have the proper release tool and had to make something. It looks like a tuning fork that goes into the slots on the side of the female connector and pushes back the retainer tabs.

 

The screws are Phillips head so you need a shorty screwdriver or, again IIRC, what I used was a tool like Matco tools part number RSD5A.

 

After much hassle I have completed the job and offer these notes to the next person that has to remove the heater core.

1. Remove the hoses from the inlet and outlet of the heater core. If you have to change your heater core then it must have leaked so you don't have to worry about draining the fluids. To remove the hoses the retaining clips used on my truck had a tab nearest the firewall that you could press with your thumb and fore finger. The problem is the reach. If the hose is still intact then it is no problem to pull after releasing the tabs. It is best if you push the hose toward the firewall then release the tabs and pull the hose off.

2. Remove the bottom cover piece under the glove box. There are two plastic rivets with center screws (don't know the technical name) that hold this piece up. The back center support simply slides onto the threaded end of a screw in the firewall.

3. Drop the glove box out of the way by pressing in at each corner to allow the stops to pass through the opening.

4. Remove the vacuum operated Floor/Panel Door actuator.

5. Remove the electronic blend door actuator.
There is a retaining screw in the front as described in the manuals. Remove the screw. The actuator is mounted to a plastic plate with a piece that holds the heater core tube against the fire wall. This entire bracket should rotate counter clockwise a little. It has keyholes cut into it. Two screws with washers go through these keyholes. In my truck they were too tight so I ended up removing them. Thats when I found out what was going on here. A third screw is the pivot point. The problem is that in any case you must remove the actuator because the actuator shaft is not going to allow you to pivot this plate. Remove the actuator by pinching the plastic holders together and lifting. It wasn't difficult. Then the plate should rotate. If not loosen the screw nearest the front and the screw that is to the right and toward the firewall. The plate should then rotate out of the way.

6. Remove the heater core cover.

7. Remove the heater core.

There you go.

 

Good one, you got those hoses off without having to use that special tool.
Thanks for the update.