Complex sentence: Until 1974, these missionary dioceses were under the metropolitical oversight of the Archbishop of Canterbury and then for seven years under an "ad hoc" Council known by the acronym CASA (Consejo Anglicano de Sud América) which also had Brazilian members.
Split into simpler sentences: Until 1974, these missionary dioceses were under the metropolitical oversight of the Archbishop of Canterbury. For the next seven years, they were administered by an "ad hoc" Council known by the acronym CASA (Consejo Anglicano de Sud América), which also had Brazilian members.