The Riviera was redesigned for the 1966 model year. It retained its cruciform frame, powertrain, and brakes, but it wore a longer, wider, more curvaceous body, a shell it now shared with the Oldsmobile Toronado, and, a year later, with the Cadillac Eldorado.
A notable styling point was the absence of vent windows, a feature GM had introduced with a flourish in the 1930s. Headlamps remained concealed, but they now pivoted up above the grille when not in use. Unlike the Toronado and Eldorado, the Riviera retained a conventional rear wheel drive layout. It was now some 200 pounds (91 kg) heavier, so acceleration with the unchanged 425 engine was slightly slower. The Gran Sport package remained available as an option. Rear seat belts were optional. AM/FM radio is optional.