It is my impression that the new replacement windshields are thinner than the originals. (Most likely a discussion on the 67-69 Barracuda Group site) If you can still use your old rubber gasket, it may not seal as well because it will have taken a set to the older, thicker dimension so a fresh gasket would be advisable.
I remember at the Hemi Reunion about 5 years ago at Quaker City...there was someone selling thin "Hemi" A-body windshields for something like $400-500 each. It made me wonder if they were just thinner modern replacements being flipped for profit. I'm always looking to reduce weight too so the thought has crossed my mind.
