Not all secret option codes are created equal, and in the late 1960s, Chevy had one so utterly and amazingly absurd that it would literally be illegal today. It was known simply as L88. Very few people knew about it -- a fact that Chevy was happy about. The L88 option got you an absolute monster under the hood that was never intended for street use. Instead, it was built for GM's top racing partners, who were to use it for their assaults on races like the legendary 24 Hours of Le Mans.
Still, this was back in the days before environmental regulation took hold in the auto industry, and if you knew what you were doing, you could tell GM you wanted the engine, and it would grudgingly oblige. Today the car is more myth than anything else, if only because so few actually exist out in the wild due to its secrecy of the time.