It is GM's pic, used more to illustrate the mounting points than an exact. The brackets changed in 1951 with the new Venti-pane doors but the screw locations are consistent location wise with a couple minor changes (they are still RH/LH specific). If you are missing the top piece as described you will need to fabricate something as the inner spot welded door parts are not reproduced. The 51-55 1st Series is shown below:
https://www.flickr.com/photos/advance-design_parts_co/14200833753/in/set-72157631868452754