I think the advice to get new axles is good, but like you, I prefer the challenge of resurrecting old equipment, the search for parts is part of the "fun." I had an '85 Wilderness that had 13" star wheels. I was advised to have my eye out for extra wheels. Didn't have it that long so never needed any. I did rewire the brakes to the star system as the 13" brakes weren't that effective.
As noted in my signature, I've had a 1965 Chevy Van since 1970 and in '88 converted it to a tow vehicle by installing a 292 ci 6 and a TH350 trans. Parts aren't easy to find but as a member of the Vintage Chevy Van Club, you get a lot of help finding them. You also have to figure out how to make the old parts if they aren't out there. Still have it.
btw- does your '79 Sierra have a 292 motor? They are towing monsters.
