Chances are, of he called them sandcasts, he knows what he has.. and is probably kidding or pulling your leg..
Look for broken cases/fins, not engines that turn over..
If you honestly have to come to a forum to see if 5 diecast motors (let alone sandcasts, AND with carbs) and a custom frame are worth 800 bux, you are simply put.. NOT READY to do this.
Myself, I will be the first to congratulate you of even 2 of them are sandcast.. Frame is maybe NICKLE plated..??