Really fun looking truck, and your nailing that box !
So for the angled windshield, since your cab is metal I'd try something like milliput. Its a 2 part epoxy putty akin to jb weld but used in the hobby world mainly. Its easy to apply and work shapes into before curing .
I'd try to roughed up the area for some tooth, mix the putty together and apply to the windshield frame from the center outwards. Moisten the putty slightly allows working time and smooths it very nice..
Just a thought