OK, I'll help you on some of them.
Frame: Have it sand blasted. Don't take it apart. Sure there'll be places the sand blaster won't get to but there's no sense fretting them.
Cab: Don't have it sand blasted. It will warp the metal. There's going to be a dozen people post after me saying I'm wrong on this but I wouldn't chance it on my truck. Acid dipping is the way to go. It will cost a little more but your panels won't be warped.
Patch panels: They are close to the correct gauge and most of them are close to fitting but they'll all need some tweaking to get them right.
what parts I have to save from the old pinion.
Save all parts of everything on the truck until you are done. By the way, take lots of pictures of disassembly, video if possible.
Brake drums: the machine shop will tell you if they are turnable.
Springs: Have them re-arched at a spring shop.
Distributor: Sounds like hardened greased. Clean it up and try again with fresh grease.
If you haven't done it already, get a reprint of the shop manual.
For GMC specific stuff, go to oldgmctrucks.com