11 Nov 2021
Roofed.

OPGI was not particularly helpful. They could just tell me that the kit contained front, rear, and middle braces. I'd have thought the middle brace was the one I needed:

(random picture from the interwebs, don't know source)
I think the unknown "middle" brace is for a Chevelle (see this Chevelles.com thread with a pic).  Regardless - the set got returned.  It does not appear that the middle brace I need is being reproduced, nor the equivalent for the longer-roofed vehicles.

 
So the logical next step is to make my own.  It ain't got to be pretty.  Cut a sheet of 22ga (I'd have preferred 16 or 18ga but didn't have it big enough).  That strip is 3" wide by 27" long.
Cleaned up the edge a little with a file.

Used the flanging tool to put a nice bend on the edges to add some strength.
Test-fit.  Cleco at the back, front wraps around a flange.

This needed to have more of a bow to it.
Used the bow I had in each of the holes to identify the range that was valid for each of these clips. 

Paint, too.
Test-fit.  Acceptable.
And then the welding starts.
Weld, weld, weld.  Skip around so nothing overheats.
Grind the welds.

Also I cut a small bit of metal to match the back edge of the roof to the B-pillar and welded it in.  This looks a lot better.
Started grinding the welds in the rear window area.  Ran out of daylight, more to come.

Go back to the previous day (6 Nov 2021)