I found this on a Pontiac site......1963 Catalina 421SD "Swiss Cheese". By 1962 Pontiac was the dominant manufacturer in both NASCAR and NHRA drag racing. As the 1963 season approached, competition from other manufacturers was fierce, and in order to maintain their dominance Pontiac engineers upped the ante by producing a handful of lightweight, all-out race cars. Aside from using aluminum front fenders, hood, inner fender wells, radiator core support, bumpers and bumper brackets, the exhaust manifolds, bellhousing, and rear axle center section were also made from aluminum. More weight loss was achieved by eliminating all non-essential equipment, soundproofing and body sealers. If that wasn't enough, the frame was lightened by drilling approximately 130 holes and eliminating the boxed rails. Upon seeing the car for the first time, a journalist referred to the frame as being "like swiss cheese", and the name stuck. Conservatively rated at 405hp, these were all-out race cars and not designed for street use. Only 14 "Swiss Cheese" 421SD Catalinas were built before the January 1963 AMA ban on factory racing activities came down.