WOW! Your truck is spectacular! Your brackets are different than mine, though. Plus, I covet thy center tailgate hinge.
As owner, operator, labor force, and bookkeeper of Pilothouse Interiors, LLC, I put a lot of interiors in trucks that looked like that. Many of them went to members of the club. My truck (1951 B3C) was respectable, but not as beautiful as yours. Included a couple photos of interiors I did for club members. The brown or saddle colored interior, for a B Model without the corner glass, were harder to do. There was no forgiveness in the fit. I think that was on of the reasons Dodge went to the 5 window design???
The second photo from right shows how I closed the cutout on my taillight. There's a change of angles in the can and that makes enclosing it a bit more challenging.
Thanks for the photos of your truck. You should be proud of it.
jc