Buick built fewer than 700 examples of the original 1970 GSX, a Grand Sport-based muscle car so quick it later sparked a magazine controversy over whether it actually out-accelerated the Hemi ‘Cuda. Backed by slogans like A Brand New Brand of Buick, the GSX carried Buick’s big-block ambitions through 1974, when the 455 V8 was dropped for good. Read on to see how Buick’s rarest muscle car nearly out-ran a Mopar legend.