After installing the duct panel the shape was returning to the panels on either side of the grill opening.
But before continuing with panel straightening , repairs need to be made to some small cracks on the bottom right (passenger) of the grill opening.
The metal here is quite thin. Using a piece of copper to act as a heat sink and helps reduces the risk of blowing holes through the metal. Drilling a small hole at the ends of the cracks helps prevent the cracks from growing. I was quite nervous welding on an outer panel (even though it will be cover by the grill).
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This gives some strength back to the panel and now the beatings can begin!