It looks to me as if the forcing cone has been re-cut[or cut?]and the back of the barrel has been dressed,likely for proper cylinder gap. All of which lends some credence to the idea that the barrel has been changed[along with the "two tone" appearance]. It could be a trick of lighting and camera. However, my '63 Python and my '80s Pythons forcing cones are not as deeply cut as the one in question, and the forcing cones and barrel ends are blued not left "in the white".If I had a dog in this fight I'd be collaring him and pulling him out of the ring! Nick