I believe you'll develop speed via strength work which includes hill running, either repeats, or running hilly courses as the Kenyans do on a steady basis.
Bill Rodgers is a former professional long-distance runner, best known for his success in marathons. He won the Boston Marathon and the New York City Marathon multiple times, solidifying his place among the most accomplished marathon runners in history. His contributions to the sport and his athletic achievements have made him a revered figure in the running community.