How to cut out rear wheel wells (radius wheel)

I'm sure a 53 GM truck fender is a totally different metal to work with. What I did on it was use a 1/4" metal rod to create the arc I wanted. Tack it inside the fender and then cut slowly with the cut-off wheel. I took care to take measurements and tack in the same spots and made sure the rod was the same length on both sides.

Just an idea but I think it will be much harder on a Barracuda wheel area though.