Denny,
The bow here is not a Z like the '50 would use. It is a U shape with 7 screws in it over its length. It works by squeezing the back cardboard under a flat edge and the front slides into the U. As for the cardboard it is completely different with slots in it to clear the screws on the various surfaces including the door weatherstrip. I believe it is these slots that give it enough extra length on the sides. I had my weatherstrip in, I just trimmed and tucked during the final fit, basically trimming off the slotted holes on the sides.
https://www.flickr.com/photos/advance-design_parts_co/18614309870/in/album-72157631867396207/I did this install before with the Z type trim and corresponding headliner and I was not happy with the results. So I cut (spot welded in) the top bow set out of a parts truck and to Chevrolets credit it is a better set-up but would have added to production costs. This cardboard set was just weighted to straighten them, I did not use any spray formula to mold them as has been described in previous posts here on the bolt.
