Complex sentence: Each week, Clark would profile a different artist from the Rock and Roll era and count down the top four songs that week from a certain year in the 1950s, 1960s or early 1970s.
Split into simpler sentences: Each week, Clark would profile a different artist from the Rock and Roll era. He would also count down the top four songs that week from a certain year in the 1950s, 1960s or early 1970s.