I did a section of mine (starts at post 54)
https://67-72chevytrucks.com/vboard/...=825127&page=3
Took a lot of sanding, spot weld cutting, and chiseling to remove the bad section. The parts are available, so I got one (at the time I found the last one in the states for above drivers door) (Used American Metal Direct). I have heard some folks have issues with the replacement pieces not being long enough, but I cut the new piece and only used what I needed. I used a 3m bonding adhesive rather than welding since it wasn't super structural and I didn't want to chance warping it. I did one small tack weld to join the 2 sections and JB Welded the seam. Mine was above the door, but I imagine it can be done that way across the windshield area also. Make sure you use a good seam sealer afterwards. To keep the water from getting in again.