Jerry, Make sure when you trim out he rust, to get to good metal. Rust does not weld well.
My 72 Charger had the rear body lines wiped out in bondo. I knocked all of that out and made sheetmetal pieces in a bender to put the body lines back in. The edges by the wheel well radius, I made cuts every 1/2 in. or so and genlty bend them in to fit the radius. after wire feed welding ,it ground down pretty smooth.