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Performance wise it would have to be a 1966 427 powered two door Biscayne sedan as that was the lightest car with the biggest baddest motor made in 1966 by the factory; though the 350 horse 327 in a Chevy II would blow it's doors off in a drag race. On the street that would be your best combination of a factory built car. It offered a fairly stiff frame and body combination that with added cop car suspension could road race or drag race or run the high bank oval as it was still comparatively light (comparing it to the four door Caprice, not a Chevy Malibu or a Chevy II that didn't weigh much more than a VW Beetle made back in 1966).
In any form of racing (performance) it is all about power to weight ratios. Of course all the power in the world does you no good if you can not get it to the ground or keep the car headed in the direction you want to go in, which is where the B-bodies frame beats out it's lighter competitors.