I'v helped my brother do 3 chop tops and you usually get rid of the vent window for a one piece side window. we made cardboard templets and brought them to a glass shop which cut the tempered safety glass to size. We've only done pre 48 cars and never had to deal with a curved windshield the only problem we had was a 48 chevrolet we had to use a two piece front windshield that was beveled and glued together in the middle. that car was done over 15 years ago and still has that window and it dosen't leak. My advise is to go to and old glass & window shop not one of the newer replacement window places.