As far as the engine goes, it seems it has been sitting for a while. So, unless it is puffing smoke when you crank it, or puffing out steam, leave the valve seals, and head gaskets alone. If it's doing a lot of clicking, you might need lifters, but a fresh oil change with some Marvel added just might free them up. Change the oil again after several hours run time. A new thermostat and water pump is probably a good idea, as well as all new belts. I'd leave the engine AC, you will be glad you did. If you think it's sucking too much power going up the hills, fine, turn it off going up the hills, and use it all the other times. As far as the brakes are concerned, check it all, if it's working, leave it alone, except for maybe changing out the fluid and surfacing the front disks and rear drums. As far as the trans goes, another cooler isn't a bad idea, but I would change out the filter, inspect what is in the pan, if nothing there, replace filter and gasket, then take it to a shop that can suck out the fluid and refill it as it circulates, this way the torque converter gets fresh fluid too. I really don't think you will need a steering cooler on it, I would however jack the fron off the ground, take the lines loose and drain all the old fluid out, turn the steering to make it push out fluid from the box. put the hoses back on and fill with good fluid and circulate till no foaming. It'll make a mess so make sure to wipe it off good, so no fire hazards. Back to the brake work, it would be a good idea to replace the rubber hoses going to the brakes. Esp on the GM's, if they have sit for a while, they have a tendency to collapse and lock the brakes up.On that 14 bolt, other than changing the fluid, you might want to replace the axle seals. I saw where you said you needed to replace the drive shaft, why? as long as it isn't broke, chuncks knocked out of it, it should be fine. I think you do have a two piece drive shaft, but the carrier bearing can be replaced and make the driveline smooth again. Yeah I would replace the u-joints too.Back to the engine, I would replace the valve cover gaskets, they are most likely dried out and will leak. As far as the carb goes, should be a quadra-jet. Good carb, but since it's sit for a while, a good rebuild is probably needed. If you've never rebuilt one, I'd suggest finding someone to do it that knows them. Those "flapper " things you see on the exhaust, are called risers, and yes, they are supposed to help warm the engine up. Most likely they are frozen. I'd take the exhaust pipes down and make sure they at least stuck open. If you remove them, it's a pain in the ass to get the exhaust to not leak. plus, you'll have added expense in exhaust work.
On the inside, you are talking about taking out a of of the convenience items. Such as the kitchen stuff, shower, and so on. I didn't see mentioned anything about the furnace and water heater. Think about how you and the family will smell after a weekend during the summer, with no shower. The Flats, The SHOP, The gulches, Compound offroad, and others, there are no shower houses. Preparing food when it's cold or when it's hot, is a lot more difficult with out a kitchen. But I do see the need for more counter space. You may want to take a look at The taco truck build. He really simplified his cooking arrangment. If the fridge works, I'd leave it. I know it's small, but you can put a lot of food in one of those things. You'll still need a cooler for drinks IMO. Does the generator work? Does the fridge work? If you are dead set on taking the fridge out, and it works. I might be interested in it if we can agree on a price.
Another thing I forgot is the fuel tanks. Since you already know you most likely need a carb rebuild, you need to protect it. Chances are, the fuel tank has rust in it. So at minimum put filters on them near the tank, another at the engine, and there is one also in the carb.Better to pull tank off and clean it out. that too is a pain in the ass, but will save issues down the road. Put clear filters on it to begin with so you can see what's getting in the filters. Who knows, you might get lucky. Another thing I'd change is the fuel pump. Cheap and easy, what you don't want happening is gas going into your crank case. The diaphragms tend to crack when they sit for a long time.
Definitely looks like you have water damage. caulk all the seams and get some coating stuff from a camper place.
