I am answering my question. After examining thousands of photos, my conclusion is that longitudinally, the door is flat. They appear to be flat between the ridge around the wheelwells. Replacing door skins sounds simple until one ends up with buckling of the skin while MIG welding. I am keeping my old skins and work them with lead to get a perfectly straight surface, only curved in the vertical direction, which stays constant between the ridges around the wheelwells. Also, A simple and logical design.
