There was no Ford factory issued STOP (cut in the glass) lens. What you have is 70's bad repro. The original STOP was a die cut steel piece that is still offered by reputible dealers such as Bratton's. The STOP die cut piece is inserted between the lens and the stop light body with thin gaskets on both sides.
Not sure what the finish of the incert stop plate was originnally, but the one that I nearly have ready to sell here is now black. Still need to rivit the brake light contact back in then repaint the outside. Or atleast I would think that rivit was painted with the back of the licence plate holder. Rod