Walker had some international racing experience early in his career in the Australian rounds of the Tasman series in 1964-65 on challenging tracks like Longford and Sandown at a time when most Australian National 2.5 drives were near world class and he also drove a Lotus 70 in the 1971 Australian rounds.
Walker tivo algunha experiencia de carreiras internacionais no inicio da súa carreira nas roldas australianas da serie Tasman en 1964-65 en pistas como Longford e Sandown nun momento no que a maioría das unidades do Australian National 2.5 estaban preto de clase mundial e tamén pilotou un Lotus 70 nas roldas australianas de 1971.