Braytak, you can probably try to fill the gaps in with paper mache. You can always sand it to blend in with the rest of the helmet. If you want your visor to be removable/replaceable, you can drill holes around the edges of your visor like every 2 inches or so. Then using he drill holes in your visor as a template, you can hot glue and embed the female side of chicago screws into the paper mache. When the paper mache cures, you can screw in the male side of the chicago screw into your visor with washers to hold them in.
I used a different type of screws on my Boba Fett helmet but the concept is exactly the same.
I used a different type of screws on my Boba Fett helmet but the concept is exactly the same.