I did that on my 57 3100 with a visor I got from Classic Parts. I remember priming and painting it to match the color.
That was fun as I did not know what color it was! I went to a paint shop and ran through a ton of books looking for something close and got lucky and figured out it was a 1979 Ford All Other Models
Paint: SS-Bright Blue 3J 1979. Had them mix me some up and it was a perfect match. Apparently the previous owner just painted it some color blue.
But All I remember about mounting it was having to drill holes and I did put a strip of foam tape between it and the cab but that may or may not be a good idea. It could promote rust or something. But seems to be OK so far.
I just looked at it and it seems that I put the two outside ends about even with the rain drip edge on the side windows. Seems like I remember possibly proping up the middle with a 2x4 or something or a cardboard box just to help hold it.
But I believe I may have screwed in the center hole first as close to dead center as possible and then did the far edges to get the right curve and positioning and then drilled the rest of the holes and screwed them all in.
I would have only had my wife to help as my son would have been too short at the time.
Mine used screws to attach with.
It did not seem to be that hard. Seemed to come out ok. I have the bottom reinforced center section sitting right down close to the stainless window trim on top of window. Maye 1/16 inch away from it.
I see now that the spacing along the top edge against the cab top is even except at the extreme outer ends where the tops curve did not quite match the visors curve so I had to live with it being a bit off. Hard to tell from the picture but it is where the glare is on the corner.
Here is a picture:
Stacey's 57