I'm not sure if I have said this in your thread yet or not. I'm not trying to talk you out of putting a visor on it at all. They give these trucks a pretty cool look for sure. There are some things to worry about though.
1. Visibility-you won't be able to see things above you as easily (stoplights or other things of the sort)
2. Leaks-if you do it right, it won't leak at all, but you will need to make sure you put sealer where you screw into the body. If it leaks, your floors and possible roof will rust out.
3. What if you decide to remove it down the road? The only way to fix the holes correctly would be to weld them shut. Then you will need to paint at least the roof again.
Not related to the visor at all, but some paint work to think about.
Does every panel need to be painted? If you plan on doing the whole truck the original color, maybe you could get by with just panel painting it, just get color samples and pick one that matches.