Complex sentence: His personal best in the 1500m was 3:57.8 when he came 1st at the 1947 South American Championships, he also came 2nd at the Championships in 1943 and again in 1949.
Split into simpler sentences: His personal best in the 1500m was 3:57.8 when he came first at the 1947 South American Championships. He also came second at the Championships in 1943 and again in 1949.