Im thinking 20ga also. Its pretty thin stuff.
The front of the fenders is an easy patch, no crazy curves. Im just looking at my 62, its a simple right angle from the top of the fender down for the flange. Two ways of doing it.
One is make the top sheetmetal, curved to follow the "L" shape, the top is curved out and the vertical section is almost flat, maybe inward some. Later cars might have an outside curve for the vertical section, they liked to get fancy with aerodynamics
Then make the lip and weld them together. Oh, and that joint, you will never see it. I can weld up sheet metal joints so you wont know where its at, after some clean up of course. Im not THAT good LOL
The other is to make the "L" shape but have the extra amount needed for the lip then hammer the lip over. It will hammer down just fine. But you have to be careful right at the peak, the point of the bend. It will be pointed at first, so you start your bending there, dont start at the ends and come up. Clamp the two ends down so they dont just spring up when you make your flange. So curl the peak over in a rough shape and work down on each side. Always coming back to the top peak. You are stretching the metal out from that peak. Oh, make the lip wider than it should be. If its a final lip of 1" start with 2". You will trim it to size.
Light taps with the hammer will give alot of movement.
I do this with 16ga and its a bear but works, 20ga will be a dream. Its a time thing, take your time. And dont worry about too much spring back. You could be outta size for the extreme ends a lil, the important area is the peak, where the fender side becomes the fender top. You get that line right and all the rest will follow.
Just simple sheet metal work. I usually do it better than I write it LOL JR
Oh, and DONT cut out anything till you are ready to weld in new stuff, what you have remaining IS your gauge...
