He had a long career as a manufacturing executive at Ford Motor Company until his retirement, then joined Nissan as head of North American operations.

After graduation from Texas A&M University in 1948 he began to climb in management, making the rounds through Ford assembly plants in Atlanta, Georgia, and Lorain, Ohio, during the 1950s.

He lived in London, Ontario, Canada, where he supervised the opening and staffing of the Talbotville (St. Thomas) assembly plant which begun operations in 1967.

Benefield had been head of the Ford assembly plant in Dearborn, Michigan when he joined Nissan North America as the organization's first vice president of manufacturing at the bequest of Runyon.

In July 1989, Benefield successfully defeated a United Auto Workers union drive attempting to organize the Nissan Smyrna plant.

TVA managed not only nuclear plants, but ran recreation facilities, tested electric cars, produced fertilizer, and even owned a herd of buffalo—in all, more than 186 separate business units.

The staff reductions earned him the sobriquet "Carvin Marvin" which inspired a satirical song played on local radio stations.

The TVA of 1933 run by engineers and bureaucratic experts was handed over to a financial class of managers who gained newfound status in the Reagan era.

Runyon's first goal was to treat the United States Postal Service as a business geared toward making money and pleasing customers.

After leaving the United States Postal Service, Runyon started an independent consulting business in Tennessee, which he operated until his death.