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...they're good, solid, Japanese production bikes from an era when quality mattered. I've had one or two myself. But none of this C+V classic steel stuff sells at much of a premium any more. If everything works, and the rubber parts and mechanicals are in good shape, maybe $250-300 to a buyer who, like your great uncle, is pretty tall. That's a very large frame. So it might be harder to sell. If I were you, I wouldn't spend a whole lot of money or time making it better. You won't get compensated for that when you sell it. Maybe clean it up (little investment there), and see if everything works (it might).
Then advertise locally on CL for $150 as is. Be prepared to take less, because anyone who buys it with the intention of riding it will have to put time and money into it before doing so.