The visor looks straight in the first photo, but I can't see the gap you are referring to in that photo. Can you take a close up and post it?
The visor looks good in the picture of it on the bench.
The visor looks bowed in the middle in the last two photos. I believe the problem is in the header or possibly in the roof line itself. Do you have a filled roof? Did the windshield posts get pulled in towards the center when the top was chopped? This could possibly cause the center of the roof to be bowed and then cause the visor to be bowed when installed.