On the fender question, I used fiberglass fenders so mine don't fit all that well. I don't believe there was anything between the cowl area and fender. Same for fender to running board. Around the front core support and fender, there is cloth covered bead used. It's the same material used around the rear fenders to bead seam.
All trucks used black fenders and running board, no matter what color truck body was. The exception was special order commercial use trucks painted to the customers specific color combination. The head light buckets were also painted black.
The cowl vent does use a spring to index it. I will try to get a picture of mine, send me a private message with your e-mail address so I can send pictures to you.
Joe
