George was not hunting for a classic when he spotted a Buick Skylark with a for-sale sign in Lisbon, Ohio, in the summer of 2014; he just stopped for a closer look. What he found was a GS455-powered GSX tribute car with its original numbers-matching 350 engine stored safely away, parked in a garage alongside a small private muscle car collection. Read on to find out about the one-of-a-kind GM production mistake that makes a factory GS455 Stage I Skylark one of the rarest muscle cars of 1970.