First you list 47-50 as your span of years and there are some real differences here.
1947 and 1948 (some early 49's) use a screw on center bow, this bow attaches to another spot welded inside the cab.
https://www.flickr.com/photos/advance-design_parts_co/18770380205/in/album-72157631867396207/
The later bow shaped like an "S" floats and the cardboard essentially holds it in place. If you do not have the early style as shown you need the "S." The early also uses a different cardboard set that is cut/notched for the screw-in bow.