There were several successful attempts to build a convertible ZR-1, most of them by private people. The DR-1 was a GM prototype to test the structural integrity of the ZR-1 chassis when it would be topless. The car was built by American Sunroof Corporation (ASC) for Don Runkle, who was the vice-president of Advanced Engineering Staff, which explains the “DR-1” designation. This car was a standard convertible that was transformed to ZR-1 specifications.
GM wanted to test if a production ZR-1 convertible was feasable, but tests showed that the C4 chassis wasn’t stiff enough to withstand the power of the LT-5 engine.