Update:
Two nights ago I pulled an all-nighter from 6:30pm to 6:30pm...mostly because I wanted to put everything back together while it was all fresh in my head from dismantling everything to get the heater core out.
Success! Today I had a chance to fill the heater core, fill the top line running into it with coolant...connect that line back up and fire it up...I should probably burp a little more air out of it but I have heat...lots of it and no foggy windows.
Huge thank you to everyone for the tips, details and motivation.
This is no simple job but just digging into it is the best thing to do.
Here's a couple of things I had to discover on my own...could be for 1984 Limited Wagon only1.
Passenger mirror lever and cable: The cable that runs from lever on the dash to the passenger mirror was in the way of dropping and reinstalling the heater box. I didn't know what it was at the the time until it was too late. I was able to get the box out without disconnecting the lever from the dash...but it was when I was putting the box back in that I pulled hard on the cable and tore the lever right through the dash. Cracked a bit out of the hole that holds the lever and ring in place...but no big deal...i was able to reinstall it all after but the dash could have been way more damaged...so I got lucky.
Had I take a few minutes to trace that cable to the source, I could have unscrewed the ring holding the lever to the dash and that would have given me plenty of room to move the heater box in and out.
2.
Heater element in the heater box: The instructions in the write (which are amazing) were followed to a tee...and in there it says to disconnect two wire plugs on the heater box. This is true, but I would add that you should remove the two bolts holding that little heater element completely before pulling the box. There is not much room in there and when pulling the box out you can damage the contacts and wires on that element. Two bolts, easy to get out and then you can pull that element out before any heater box movement.
I tested this out by removing the element from the heater box before installing the box back in...I didn't have to worry as I was manhandling the box back in place and sure enough once it was fitted I had easy access to putting the element back in and putting the two bolts in.
3. Foam - I was feeling a bit paralyzed leading up to the work because I wasn't sure which foam to get. I had limited selection here in town and nothing seemed to make sense. In the end I went with some high end closed cell foam tape of varying dimensions...from 1/8" to 3/4". I cleaned the box well...used the tape foam and it all seemed to adhere really well.
Wish I wouldn't have over thought this that much ahead of the work happening
4. Big foam - My foam door (the large one) was in great shape but wasn't seating well in one position. I shaved the sides down where it came in contact with some rivets and that took care of it.
Glad it's done. I also swapped out the blower motor and fan for new ones...so no more squeaky blower motor. Winter can be enjoyed even more now in the Eagle wagon.
Cheers and again...big thanks to you all for your help!