I have a '72 C10 that has served as a daily driver at times in the past few years. Its really my primary backup vehicle these days.
I've spent some money on maintainance over the years, but probably spent more replacing the tires than all the other work together in nearly 10 years I've owned it.
It made a 3,200 mile road trip a couple years ago without missing a beat. I would not be afraid of one of that era truck and if you maintain it I'd expect years of useful life. Mine is rusting away and rust is probably what is going to stop it. Once a door falls off I'll probably start parting it out.