Today I go through a door skin removal. My original passengers door had rusted through in the front bottom corner, which is a common place for the doors on these cars to rust through. I bought a different old door that appeared to be in good shape (passed the magnet test and all), it just had a crease in the front that the seller (and old body guy who restores Mustangs) said would be easy to remove with a stud welder. Maybe for him, but not for me. Also turns out there was still quite a bit of filler on the door and some rust spots. All of this was on the skin. Since the skin is such an easy fix and a new skin is cheap ($50), I opted to replace the skin. I'll probably do this for the driver's door too as there are many dings in the door.
After receiving the door I dug in to see if I could locate rust or filler, which I did. Turns out the door was not looking so great, and the crease was a very difficult fix. Not worth it.
The firsts step in door skin removal is to go around the entire edge of the door with a grinder and grind away the skin where it folds over the edge of the door. This will break the skin away and it will start to separate as seen here.
Once I've ground the entire edge of the door and cut through half a dozen spot welds, the skin lifts off.
As the pictures show, even though it's a reproduction skin, it fit nicely and the door will look brand new on the outside. The skin has a few dings from shipping (and I think I gave it a new one tonight) but they are minor and nothing that can't be worked out with a hammer and dolly.
Now that I know the skin fits, I can be at ease and concentrate on the next step...this rusty inner door. It's not pictured, but I then hit this with a wirebrush on my angle grinder to remove all the rust. Next I'll degrease it, spray the entire inner door with a rust converter, paint it with some rust encapsulator, reinstall the window and regulator and door handle/locking mechanism, put some rubber undercoating on the inside of the door skin for vibration dampening, and weld the skin on. Put a few coats of lacquer on the interior side of the door, install the new window felts and seals, and finally the panel and this door will look brand new. All this to come...