I'm not familiar with the E bodies, but all the others from that era were a rubber gasket as far as I know.
I also used the knife for many years.
I now have the tool made for windshield removal.
It's simply a handle with a sharp angeld blade at one end and a handle on a cable at the other end.
Insert the blade and carefully pull it around the glass.
Viola. The glass can now easily be removed.
It is very helpful.