[Ed in Maine]

I understand what you said about being very rusty but if the fender mounting studs are good, I would cut the original panel about 1/2 to 3/4 of an inch below the studs. This way you don't have to worry about getting the new studs accurately placed. Like Oldbluoval mentions corrosion can be a problem. I like to use a "vice grip" type tool to put a step in the sheet metal and insert the new panel behind the original metal. Then seal weld the outside of the seam. Tac the inside of the panel every couple of inches for added strength. Then, after painting, caulk the inside to prevent any moisture from getting into the seam. Grind down the welds smooth on the outside and fill with body putty. Good luck, Ed