imperial,Hi, I am an "old glass guy". been doing it for 45 years. The last w/shield I cut down was a pro-street 55 Chevy a few years ago. It was a 4" chop and the w/shield looked like a banana when I was done with it. Cutting down a w/shield the traditional way,with a glass cutter ,the glass can "run out" ahead of the cut, as you are working against built in stress's in the glass(more so with accutely curved glass). With that much curve it's very risky even handling the glass after it's cut down. Moreso if you were able to sucsessfully cut down a speedster w/shield it would be very vulnerable to cracking if not supported in a frame across the top. I think some shops have used a water jet, or a cut-off wheel to cut glass,but I have never been involved the process. The deal in the past was, the customer buys the w/shield first and we try and cut it down with no guarantee.(usually not a good outcome for all parties involved!) As far as tempered glass goes. Untrue, you cannot un-temper glass.That glass starts out as ordinary float glass and then it goes through a tempering process in an oven. Once that glass is tempered it becomes very strong(hardened) but if you were to try and cut it, it would shatter. Both laminated and tempered are considered safety glass. Laminated for the w/shield and tempered for all the other windows. There you have it auto glass "101"