Actually John,

This looks like him. His death certificate should tell you details of any marriages, how long he had been in Victoria and other colonies and a lot of other useful stuff.

Digger - Death Index. Victoria 1921-1985
Surname: JOHNSTONE
Given Names: David Valentine
Father: David
Mother: Jeanie VALENTINE
Death Place: BALW
Age: 69
Year: 1966
Reg Number: 24091
Event: D

This is the record of this man's cremation.

http://deceasedsearch.com/page-o6986454-en.html

If you click on the location of the ashes it shows the ashes of another person at the location - possibly a wife.