Contact Steve at The Filling Station. A few years ago he and I worked with Steele to fix a problem they had with their door seals. Well, they sort of fixed the problem. The original seal GM used was 1/2 inch thick. Until the late 1980s they (GM) were still carrying it. It does not exist anymore. If you use more than 1/2 inch, your door will become exponentially harder to close the larger you get. 5/8" is going to be tight but it might settle down over time. You don't want the rubber too thick and there is definitely a "happy spot" where all works best. In an ideal world, we would have this run like auto makers make it today...open in the center so that it seals easily. 11/16" is just wrong and during our work I learned this thickness was used because it was assumed it would work for many styles and types of doors. It sure won't work for the AD trucks. Steel used a 3/8" die for rubber made for The Filling Station and it was too thin. I have some of that weatherstrip here. When Steele learned of the problem, they ended up using an old die for 7/16", ran the strip again and this generally works fine. During this study I used some Silly Putty between the doors and cab of my 1952 (never wrecked and with proper hinges) and the gap was 7/16" or just a hair below that, so 7/16" works okay. Note: in many of the AD trucks, the upper door clearance will be 3/8" or so...some have told me GM made this change after the first year of the AD trucks. From what I recall the doors on the first year didn't have a smaller clearance along the top and leaked water in blowing rains around the top of the window. Good luck.
