Back when I was teaching auto body work, we used a kit that consisted of a spring-loaded centering plunger and several hole saw type cutters that threaded onto the shank. They varied in diameter from 1/4" to 1/2" in about 4 steps. The nice thing about that setup was that the cutter could be matched to the diameter of the spot welds, and it didn't make a hole through the lower piece of metal. Once the outer panel was freed up, the residue could be ground away, leaving flat metal with no holes to fill. We could also drill a series of holes in the replacement panel, clamp it into place, and fill the holes with MIG wire.
Jerry
