Removing front windshield and back glass

Well, now that this subject is up, Is it necessary to remove the glass in order to properly install a headliner? I want to try a new headliner in my 65 barracuda. Can I still get new front glass for my car? I would like to change the windshield while it's out.
I think the previous owner had the front glass out for painting reasons. The gasket looks good and soft, but the glass is old and nasty. It already has a new lock strip. It does leak though..Maybe I will find the gasket damaged when I take it out.
Got 1 more show to attend before starting winter project on the car. Installing my 8 3/4 rear end...woo hooo.