The Aussies had a kid, Miles Murphy, who was still 15 when he ran 47.9 (auto). Then some years later he beat Cuba’s Roberto Hernanadez to win the inaugural world junior championship 400m in 1986. Murphy went on to break Darren Clark’s Aussie Open record with a run in 44.72, but he never reached another international tournament final. Clark regained the record which still stands at 44.38 some 21 years after he set it in the Seoul Olympic semi. Despite not having any injury or health concerns at that time, Murphy was eliminated in the second round in Seoul.
Up until then the USA’s Darrell Robinson held the world junior record at around 44.6, but in Seoul Steve Lewis wrecked that with his gold meda run in sub 44. Lewis was coached by John Smith.