I tacked the inner bottom with MIG, but chose to finish weld in Oxy-Acetylene. Much better than my cab-corner experience, but I should not have tacked with MIG, I should have tacked with gas; the MIG tacks were much harder, and did not melt in nicely when I did the oxy-acet pass. The end result, though, was minimal distortion for sure, but I made the cut just below the strengthening rib so the rib could act as rigidity (and because the reproduction panel's rib was drunk).
Also, I'll share a couple of tools I made.
First up, is my Hammer Hammer. Initially about 18" of 3/4" solid round, to help my planish the fuel filler hole patch, when I couldn't get a hammer in there. I used it as a hammer, and I used it as a dolly. Dealing with one of the West Coast Mirror holes, I cut about 1" off the end and welded it 90° to fit inside the window opening, and I hit it with a hammer to push metal out, and I used it as a dolly to hammer metal in.
And then I made this one, to pull part of the window felt flange that I buggered fixing the aforementioned hole. This hammer-smacking-flange-putter-back-inator is just 1" flat bar. I welded a tang from a file so I can beat it with a hammer, to pull the wee flange back into place.
The tang came from this tool I made, a slapping file, which does a grand job of persuading metal into perfection. Or perfect enough for a skim of filler in my case.
