Complex sentence: Prior to his declaration as a Sedevacantist, Coomaraswamy had become close to Archbishop Marcel Lefebvre and was appointed a Professor of Church History at the New England seminary of the Society of St. Pius V (SSPV).
Split into simpler sentences: Prior to his declaration as a Sedevacantist, Coomaraswamy become close to Archbishop Marcel Lefebvre. The former was appointed a Professor of Church History at the New England seminary of the Society of St. Pius V (SSPV).