It was Halberg but that gets into a touchy area. Halberg, Bill Baillie and Bill Rodger (not the US BR obviously) had gone from New Zealand to live in Australia for a while. I think it was before the 1956 Olympics. They did spend some time at Portsea but only briefly.
When Halberg began running well Cerutty claimed that he had coached Halberg. Halberg made it very clear that he had never been coached by anyone other than Lydiard and made a point of saying so in "A CLean Pair of Heels."