The wind window rests in a triangular frame with a leg down into the door shell. At the bottom of this leg there are two screws that hold this piece in place. Additionally, along the front edge of the door shell, there are three or four screws that secure the wing window frame into the door shell. All of this said, I don't think you have to remove the wing window frame to replace the wing window glass. You will need some new setting tape, in order to secure the new glass.
Try:
www.classicparts.com www.lmctruck.com www.bowtiebits.com www.oldchevytrucks.com These manufacturers, among others, carry the setting tape and other door weatherstrip, runners, seals and bumpers.
Good luck with your project and I hope this information is helpful.
Tony
