Complex sentence: Mayflower was sold to Dell Publishing in 1963, with Powell and Lionel V. Fennelly becoming joint managing directors, with Powell handling editorial and promotional responsibilities, and Fennelly handling administrative, commercial and sales responsibilities.
Split into simpler sentences: Mayflower was sold to Dell Publishing in 1963, with Powell and Lionel V. Fennelly becoming joint managing directors. Powell handled editorial and promotional responsibilities, and Fennelly handled administrative, commercial and sales responsibilities.