As for the headliner, I would say that you're better off to just replace the material than to try to glue the old one up. The foam rubber padding deteriorates and causes the cloth to separate from it, causing the drooping. On my '91 Suburban that I'm trying to get into shape now to make it my daily driver, I bought new headliner material and glue from this place:
http://www.stockinteriors.com/items....rban_Headliner
It's kind of a messy job, but I'm really pleased with the results. I used the "extra large" DIY kit with the extra width (60") material.
On your windows, all I can tell you is if you're going to replace the motor, be sure to get some kind of service manual with step by step instructions. I replaced a motor in my '89 this past summer, and I'd rather take a beating than do it again. I suppose it would get easier with practice.
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1977 GMC K25 400/400/205
1989 Chevy Suburban R1500 350/700R4 (work beater)
1994 Chevy K3500 dually 454/4L80
1996 Corvette LT4 350/ZF 6 speed
2000 Bonneville SSEI Supercharged 3.8 Liter V6
1966 Chevelle 2 door sedan (Needs major repair
)