Yep, this is one spot where more rust helps out. My drip rails were shot so off they went too. It's easier to cut the roof off an inch or so back, then you can find and dispense with the spot welds. Good luck!
It's like they used some type of rolling spot welder. Grind through most of each spot weld and then peel off the edge of the roof. It helps if you cut the roof as close to the drip rail as possible. Tedious but not hard.