what i don't like is the very aged derailleurs and cables, and the weak side-pull brakes. i really want this to be a rock-solid touring bike where i don't have to worry about having to fix anything but a flat mid-tour.
Some people replace their cables every year. And yours are how
Unless your derailleurs are actually damaged, they'll probably be fine if they're just cleaned up and have new cables. For brakes, your best bet would probably be to put Kool Stop pads on them. Your brake pads have probably turned hard and lost their grip. Kool Stop pads won't suddenly turn the brakes into modern double-pivot ones (or side-pulls which could flip the bike in the 1970's), but they will make a bigger improvement than other brands. Go to http://www.koolstop.com/brakes/index.php
and go down to about the tenth picture, labeled "Campy Replacement pad" which is probably what will fit your holders. If you might be doing a substancial amount of riding in rain, get the salmon-colored ones, otherwise get the black. Many bike shops have these in stock, or you can order directly from Kool Stop, or eBay, etc.. But as for fitting new brakes, the biggest problem, from my experience, seems to be that the the new ones have the nut recessed and require a bigger hole in the back of the fork and a thicker brake bridge in the back. Without going into all the details and what I've tried, I'll just say I haven't found a way to make it work.
I had a Blackburn rack on my tourer from the late 70's (actually we still have a couple of them on vintage bikes) which, instead of connecting to the seat stays, had a part that went over the brake bolt and was held onto the brake bridge by the nut that was normally on the old type of brakes anyway. I don't know if you can still find that type of rack, but it works well. Our older son still commutes with that arrangement, carrying loads of up to 60 pounds (!) back there.
Does your bike have room for a third chainring? And does the spider have the mounting holes for the third chainring? If not, you can get gears nearly as low as a lot of road triples have by going with the smallest possible inner ring, which for a 130mm bolt circle diameter (BCD) is 38 teeth, and then have the biggest cog on your freewheel be 34 teeth. because of the large jumps between gears that would result from an even distribution, the very low end is often seen as a "bail-out" gear, and it is common to have a 6-speed freewheel with 14-16-18-21-24-34, with a large jump between the 24 and 34 and closer spacing for the rest. Freewheels are being made even today. One source is Loose Screws
, and at $14.50 for this one, you can't complain about the price!
You might need a different rear derailleur to handle it though. Normal road ones can't accommodate a large cog of more than about 28 teeth. MTB derailleurs will work, but you'll probably want to make sure you get a high-normal type instead of RapidRise (or low-normal) which is more common in MTBs as of the last several years. High-normal is the kind you're used to, whereas low-normal has the spring push the derailleur in toward the wheel, and the shifter has to pull the cable to make the derailleur go to smaller cogs.
If your bike is that old though, I wonder if it has 27" wheels. There are still 27" tires available, but most of the best ones are not available in that size. It has mostly gone to 700c, 26", and off the top of my head I think even 650B and 650c probably offer more and better choices today.