So I acquired a 427 BBC. Casting number 3935439 with 3917125 heads. From what I hear these are NOT to be run with unleaded fuel. Is this right? Will an adative work? I hear it's worth some $$$. How much? Anything else I should know about this engine. It's been bored .100 with KB 454 pistons. 454 steel crank. Completely balanced. Just anything else I should know would be appreciated.