It was called the 965, and only such prototype exists.
This concept may look like a Porsche 959 with body camouflage, but that’s only because it was tested on public roads. Porsche didn’t want to let on that it was testing something very different at the time. Instead of the typical flat-six engine, this prototype was powered by a water-cooled V8 provided by Audi. This testing happened in the mid-1980s, and Porsche was already then looking into replacing the 911’s air-cooled flat-six.
Eventually, a water-cooled flat-six was chosen, but apparently other engines were considered. In the case of the 965, Porsche really defied tradition. Today, the one and only 965 is a part of the collection at the official Porsche Museum.