I had to have my roof on my 70 reskined because my car had a sun roof in it. I had to go find a donor car and remove the roof. I cut the roof off the donor car at the bottom of the post so I could get it home. You will have to dig out the seam sealer in the drip rails because the spot welds are under the sealer. The drip rails will not be part of the skin, they form the flange that the skin is welded to.
I took my car somewhere to have the skin welded on because I didn't trust myself to get it on and not warp it, but I heard that it is not that hard to do. My repair was a little more extensive then just the skin because the center brace was also cut out of my roof, so I had to have that also taken out of the donor car.
1970 SS 350, 4 spd, posi, black