while you are at it check the door shell for cracks, old body repairs etc. the lower hinge area is a problem as well as the small web between the inner and outer shell near the vent window lower rear area. check all the spot welds especially if the door seems to be a little floppy or, when the door is opened, the shell can be "twisted" and it isn't because of loose hinges.
check the hinges and latches while you're at it. check the lower edge of the door for rusty areas or soft spots. the replacement parts are available if required.
as far as the one piece glass, do some research because the glass has to make a shift when part way up/down. it has a tendency to bind in the track at that point or look kinda funny because it can be at a weird angle. there is a good set of videos on youtube explaining the one piece glass install and some mods that make it easier to get the glass to move properly in the track. check it out.
as far as the inner thin door shell, are you talking about the shell that is part of the window channel felting backer material? the felt can be bought at an auto glass shop or check the Richelieu site for auto window channel supplies
https://www.youtube.com/watch?v=k2_p9Ol9isE
for part one. from there you can find part 2
door lower hinge pocket repair here, to see what I am talking about and to get eyes on the problem with the lower hinge pocket
https://www.youtube.com/watch?v=H82NNtrIQqA
post 35 here also has some good pics and a new part vendor if required, plus you can see the old and new parts to get an idea of what happens.
http://67-72chevytrucks.com/vboard/s....php?p=4947159
I would say, if you have skills, tackle the project. set stuff aside in order so you know what comes next on reassembly, take pics as you go. soon you will have it apart with a good idea of what you will need to fix the problem. if the truck is running and licensed maybe drive by a glass shop to see if they have parts available to replace window channel felts etc.