Complex sentence: In 1961 it was absorbed by the legendary political and literary magazine "The Bulletin" and Coleman consequently became editor of The Bulletin between 1964 and 1967 and later editor of "Quadrant" magazine for twenty years between 1967 and 1990.
Split into simpler sentences: In 1961 it was absorbed by the legendary political and literary magazine "The Bulletin" and Coleman consequently became editor of The Bulletin between 1964 and 1967. In 1967 he also became editor of "Quadrant" magazine, and he held this role for twenty years between 1967 and 1990.