He's asking 1700. So, to him, it's worth 1700.
That's pretty obvious.
You might consider it worth less, but that doesn't change the value to him.
However, looking at Nada.com for a 1980 Chevy Pickup, in "low" condition, it's still over $2500. Few rust spots, runs well, etc.
$1700 is a perfectly fair price. A deal, even. And that's for the lowest version of the truck. If it's a 3/4 ton, or anything like that..worth quite a bit more.