Complex sentence: Still's first managerial job came with Leytonstone in the late 1970's, who subsequently merged with Ilford to become Leytonstone & Ilford, whom he took to their first Isthmian League title in the 1981--82 season.
Split into simpler sentences: Still's first managerial job came with Leytonstone in the late 1970's, who subsequently merged with Ilford to become Leytonstone & Ilford. He took the club to their first Isthmian League title in the 1981--82 season.