The original Super Duty 421 Lemans were Pontiac factory-built drag race-only coupes and station wagons. They were designed to combat other factory lightweights that had a weight advantage over the big Super Duty Catalinas. Two "mule" cars were built as Tempests, one in Silvermist Metallic and one in Yorktown Blue Metallic, which were the testbed for the production series. Eventually six Lemans-badged coupes were built (including Bill Shrewsberry''s), along with six Tempest station wagons in Cameo White with blue interiors.
In addition to the 421 engines, the Super Duty Lemans featured aluminum front sheetmetal, aluminum bumpers and a unique clutch-operated 4-speed transaxle. This transaxle arrangement placed more weight over the rear tires and allowed clutchless shifting, much like modern drag racing transmissions. Special parts on the Lemans 421 SD''s included dual 4- barrel carbs mounted on a medium-rise intake manifold, sealed aluminum cross-flow radiator with special overflow tank, and factory exhaust dumps. Other features included heater delete plates on the firewall, trunk mounted battery, and special "black box" access door to the transaxle and clutch assembly.