Most people will tell you that you need a spot-weld cutter to remove body panels that are welded on.
I actually dont like these because they cost money, wear out and you have to grind off the little circle that it cuts out: if I wanted to grind out the spot-weld, why use a cutter?
What I do is use a 1/8" drill bit to drill past the first layer of tin.
The I use a 5/16" bit with the end ground almost flat. The flat tip means that it wont want to make the hole deeper once it reaches the bottom of the 1/8" hole. It will want to stop when it reaches that point.
Then just use an old chisel or gasket scraper to separate the panels. If you hit the middle of the weld with the 1/8" bit, it does not take much to separate the panel.
Relatively un-marred panel behind
And just to prove that this works for more than emergency purposes I took an entire Miata apart with this technique.
I will admit to some cheating on this as I was getting tired of pushing on the end of the drill
