By 1973, the golden age of the American muscle car had come to an inglorious end. On New York’s Long Island, Baldwin Chevrolet had changed hands and was largely out of the modified new car business, but Motion Performance soldiered on, creating one last radically styled Corvette in the form of the Motion Manta Ray. Just three examples were built in total, of which one was crashed when new and one was later lost to history. That makes the 1973 Motion Manta Ray seen here the last known example of its kind, and on Saturday, July 23, it will cross the auction stage in Harrisburg, Pennsylvania.

Motion’s experience in modifying Corvettes began with the Phase III GT, which swapped the third-generation Corvette’s pop-up headlamps for exposed units, tucked into the fenders and fitted with aerodynamic covers a la classic Italian sports and racing cars. Other exterior changes included a revised front bumper and fascia, fender flares, side “gills” and new taillamps, but overall, the car’s appearance was subtle. Performance-wise, a customer was only limited by the size of the check he was willing to write.

A special edition of an already special car goes up for sale.