Once the roof panel was temp installed then I had to figure out getting the rear window panel integrated as well as the bed partition (or truck cab rear panel). The first part I installed was the small bow-frame/stiffener that goes between the upper and lower panels in this area. I had to figure out how to clip this part into the existing structure. I did so with some custom sheet metal clips I fabbed.
Next was the upper and lower main rear panels. In order to get both to fit properly (since they were somewhat trapped), they had to be split into two parts, a LH and RH part, and welded back together after installation. The upper window panel remained basically stock (except for the small area near the cab) but the lower panel needed to be trimmed and modded extensively.
On the lower panel, in addition to splitting the panel, I added a flange on both sides (LH & RH) to plug weld it to the inside of the cab. I also added a flange on the bottom that will eventually connect to the new floor panel in the cab.
1949 Chevy Panel Truck A Project Journal I'm old but I make up for it by being immature.