I think you may have bought the wrong panel, when I replaced mine the1947-50 replacement panel came with the louvers? Could you have ordered a 1951-54 version? Most of the cowl replacement pieces require extensive fitting work so that is not unusual. You can perhaps get louvres pressed at a rod shop but I doubt they will match the originals.
http://www.flickr.com/photos/advance-design_parts_co/8129131488/in/set-72157631867396207