These days Chevrolet uses the ZR2 badge for off-road trucks, but it once adorned a rare Corvette variant. Scheduled to cross the block at a Mecum auction in Indianapolis on May 20, this 1971 Corvette ZR2 coupe is one of just 12 built, and is thought to be the last to roll out of the factory. The Corvette ZR2 was a one-year-only affair for 1971…