When I did the top on my 51 F1 I laid the windshield back a bit and like the way it made the truck look. Check out the pictures on webshots search mphracing
I did not 1/4 the roof at all. I also TIG welded everything so I could control the heat and warping better.
I didn't want to stretch the doors etc and didn't have a doner cab for the tops of the doors and door openings in the cab.