RE: Joseph Cotten's Lincoln...
Yes, Cotten's Lincoln looked liked this car--apart from the fact of being a convertible--except that the car pictured above shows a standard taillight treatment that is vertically positioned. Cotten's car had taillights that seemed to be integrated horizontally along the top of the fender with the red plastic lens peaking upwards similar to, but smaller than, those of a '55 Cadilac.
When I first saw the movie and described it to a friend, he thought it might be a Hudson, but a subsequent viewing confirmed it is a Lincoln, though one that, I suppose, has been discreetly modified.