I would recommend Auto Custom Carpets (ACC) out of Anniston, Alabama for the carpet and lower door inserts. They also have a kick panel piece, but I don't know what the point of that is unless you want your ride to feel like a hippie van. Good domestic product made here instead of Xinjiang, China. I was able to save the carpet in my Jimmy, but my Caprice was beyond toast so I ripped the old one out, burned it, and bought one from them. OEM look and quality. If you can, use your old carpet as a template, but I know from experience if you don't want your new one touching the old one. Just get ready to trim when you get it. I imagine the door inserts are pretty cut and dry. You can order directly, or they have a store on eBay.
As far as the upper door panels and seat covers/reupholstery kits, I know LMC has all that. If someone knows a place better (i.e. Classic Parts) that has those things, I would only resort to LMC (simply because their reputation is pretty mixed in this community) as a safety or get it done locally if you would rather a professional handle it. If it's only lightly or moderately torn, you'd be surprised what a girlfriend or wife and a sewing needle can accomplish. I imagine the same thing as far as sourcing for the door handles, but there's a fellow on here that has a hook up for a guy who can carve a set by hand. Personally, I've been thinking about that for my own. Kinda gives it a look alluding to a Centurion or a Choo Choo conversion.
http://www.gmsquarebody.com/forum/showthread.php?t=8614
