Spent a few evenings making patch panels and welding. Turned out pretty decent. Alternatively, is a repo upper dash made for the Chevelle. Same windshield, Im guessing the front portion would work.
Did the same thing on my 65 Catalina. Used a shrinker stretcher to form the part, cut out all the rotten metal and mig welded the new channel in. Looks good but I will know for certain when I replace the glass.