I don't plan on removing the entire pinch weld only that portion of the tank marked in yellow on the original picture. This crud diagram might help explain. Basically I would make a small vertical cut (red line) after cutting of the portion of the tank I want removed. Rather than adding a piece to fill the gap, I would fold over B then A after some trimming. There would be overlap, so the next step would be to cut through both A and B after they're folded over to create a butt joint/seam. I expect the resulting joint to be 4-6 inches plus any collateral damage to the factory pinch weld. I'm OK with the tab from the factory pinch weld visible on the rest of the tank, although I may end up gently folding it over.
Love to hear from some guys who cut into tanks. I'm trying to keep the effect on the factory weld to a minimum. My hope is that the small new welded seem is not visible on the underside of the tank, although I'll hope to clean it up enough so that its not evident anyway. I'm OK with the cutting and shaping, but plan to find someone far more skilled with a tig welder to make sure the tank seals properly.
