Well, there were some photos of this odd option. Too bad the rest of the car was in much worse shape than the fiber glass top

There was a mention of this aftermarket hardtop for the full size pontiac convertibles in the June 2007 Hemmings Muscle Machines magazine:

"...a San Diego, California, manufacturer offered special hardtops for all GM convertibles in 1962 and 1963. They were dealer items. The hardtop was featured on the cover of the April 1963 Popular Mechanix magazine. The company, Le Mans Inc., did not last long; by mid-1963, it was going out of business. The top was fiberglass, weighed about 80 pounds and two people could lift it on or off a car. The tops came in white, black or primer ready for paint. (Information taken from Special Interest Autos May/June 1993.)"