Being a old as they are if the gasket is still orginal they become hard, cracked and brittle. Sometimes getting them out can be a challenge. It will take 2 guys working at it slowly not to crack your window. Some, not sure of the year also may have a window rope within the gasket. (not sure of yours) The last time I took one out the gasket was toast anyways, so we had to peel back the outer lip gasket and slowly cut the lip away with a sharp knife all around the windshield. Never use a screwdriver to pri up on the gasket. Use the hard but flexable plastic knife tools. Once the gasket lip is cut away all around so you can see the edge of the glass have someone lightly push from the inside with even presure. With the sides and top half loose you should be able to lift out the window.
Year One states they have your gasket...also note they have window kits.
http://www.nextgenparts.com/serverfiles/fbshopmain2.asp?cat=A