FWIW,
This is how you make fast work of the fender your have:
Watervliet Air Hammer
I had a fender that probably had a chain come loose and beat it up bad. It was pitted rusty (though no holes). The Watervliet's are quite pricey to buy from someone that knows what they have. You can spend a thousand dollars for a very complete one. But when you know what you are looking for you some times get lucky. My brother has a couple (what are you spoosed to do when its like $20 at a garage sale for a complete one?) so I tried it out. Once you got the hang of it the tool would let you move the metal fast. You still needed to know how to correct the shape as it can move the metal too much too.
Yes it is impracticable for most people. I just thought I would add the little tid bit. Now a few more people will know what the tool looks like and you never know when you find one at the right price.