There is a 1978 NEW SOUTH WALES death for a John Adrian ADAM; if this is your fellow, his death certificate should state how long he was in AUSTRALIA (and each State) which will enable you to narrow your search.
A John Adrian ADAM, student, showing on AUSTRALIAN Electoral Rolls, 1954 PARKVILLE, VICTORIA 1958 & 1963 WEST SYDNEY.
There are two marriages showing for John Adrian ADAMs; QUEENSLAND 1935 / B022542 to Irina POPOV and NEW SOUTH WALES 1956 / 7885 to Olive Rosina MCKINNEY.
Irina divorced John ADAM 1938 on the grounds of adultery, Harold MUNRO was Irina's solicitor. Irina's guardian was an Ivan POPOV; Irina ADAM nee POPOV remarried NEW SOUTH WALES 1939 / 18621 to Harold MUNRO.
Irina divorced Harold MUNRO 1943 on the ground of desertion by reason of non-compliance with a decree for restitution of conjugal rights
Olive Rosina ADAM, Librarian, shows only on the 1963 AUSTRALIAN Electoral Roll at WEST SYDNEY on her own so possibly the couple parted company.