I acquired the tool I'd been missing to move the project forward. Now that I own a spot welder I can start to reassemble the car.
The first thing I needed to do was to reinforce the "B" pillar. Metal fatigue took its toll on this connection. Since I planned on replacing the kluged roof support anyway I was able to make a permanent repair.
My solution is to install a substantial roof support and add a second "B" pillar salvaged off of the donor car. The nub of the old "A" pillar presented itself as the ideal location for the second "B" pillar, forming a very strong box that wasn't there before.
I may put glass in this opening.
I needed to stabilize the passenger side of the car before cutting away the hack work. I brazed a piece of 1 1/2" angle iron to the two existing "B" pillars and the "A" and "C" pillar. This allows me to cut away the roof support without having a 22-foot car bend in half.
I trimmed away the mangled sheet metal on both sides and the support dropped away.
Trimmed the metal back until I had a clean cross section from the roof of the first car to the roof of the second. I was going to match the exact structure in new sheet-metal but I didn't think that that shape would handle the addition span. The old support had bowed upward, slightly.
Looked around my shop for a piece of iron to better bridge the gap when I noticed one of the Unistrut pieces I used to lift the trailer body. The cross section turned out to be an exact fit. The structure allowed me to slide a piece in that is 6" longer than the opening, slipped 3" into each end. The metal is much thicker than the original structure yet will allow for some flex.