I discussed this same issue (chopping a car with curved front glass) at length with Mark Wojcik (Chopolds on the HAMB). He built a pretty heavily whacked Olds with a chopped 57 Olds roof, and his theory is that you can't chop a curved glass car much more than 2" or so of vertical drop with the stock windshield. What you can do is start to lay the glass back and simultaneously cut off a bit of the top edge, but mostly the sides so the glass will lean back. But cut too much and the glass will pull out of the channel and there will be a gap. This was what Mark hypothesized was the reason for the trim Barris added to the sides of the windshield on the Kopper Kart. The truck had been chopped too much to make the glass fit so they had to hide the gap. But nowadays, even if the factory glass can't fit, you could make a template and there are companies that will make a custom piece of curved glass for you. Expensive, but will get the job done and done right. Awesome car.