Looking at your pictures, and taking into consideration the rusty/banged up condition of your existing metal, I would form the patches to closely match the contour of the existing panel and trace the outside edge of your patch and cut out the existing metal for a tight fit. Then you can butt weld it a spot at a time, spaced out the length of the panel to prevent warping.
Carl

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission