A propane torch works well to remove the lead. There is a lead joint on the A pillar, right where the roof meets the pillar at the upper corner of the windsheild. The gutters are probably going to be the trickiest part to seperate since it is pinch welded the whole length. Although it was for a fastback skin, I found it easier to cut out the center of roof panel first. Then worked my way around to remove the front edge, rear edge then side edges by the gutters.
A cut off wheel in an angle grinder makes pretty easy work of removing the top layer of the pinch welded roof skin.
For the window frames, a spot weld cutter and an old strong sharp putty knive makes a nice seperation tool for the stubborn spot welds.
When you install the new skin are you planning to mig weld it on, or spot weld it? If spot welding you will probably want a 220V spot welder. I have a 110V that was marginal for doing the window areas. I ended up plug welding with the mig instead.