Chevrolet Chevelle SS 454 LS6
The Chevelle was always a very popular muscle car. Its combination of affordability, excellent design, and powerful engines was a hit with buyers. In 1970, Chevrolet offered an expanded line of engines, including the famous 454 V8 big blocks. The regular version was called the LS5. It was very powerful, but there was an even stronger LS6 variant. This was in just 3,700 cars. And only about 25 were convertibles (via Motor Trend).
This is the car to mention when you talk about the holy grail of muscle car culture. It is even more surprising that such an icon would spend decades in a barn under a heavy coat of dust. The original owner parked it in 1978 and forgot about it until recently when a muscle car enthusiast discovered it and got it running in no time.