Why couldn't you use an appropriate sized drill in each of the 4 corners to get the correct radius of the curve? You would want to make sure the shell cannot move at all.
Hi Gene, I’m going to try your method using a flat sheet of aluminum to see how close I can get.
For a a car shell I think a drill press would be best as @Hancock52 mentioned. The big problems would be securing the shell so it does not move on the drill press and then not damaging the soft aluminum shell with the clamps that are holding it in securely place.