All I know is that they only made 1774 SS427 Z03's. I'm confident that if the vehicle is truly untouched and in decent condition it will probably bring north of 20K. But its really what someone is willing to pay for it vs. whats it worth.
In any case it's worth holding on to it and if you need to sell it; sell it whole and only part it out if you don't get what you want.
I would love to have it because I'm cloning what you have but in a convertable but I know I don't have the scratch for it. A great score though!