I know the postcard rate was a halfpenny at this time, but would that carry it to Australia? I don't know.
For a more substantial package maybe a threepenny stamp would be needed
|1980: Centenary of Wild Bird Protection Act|
An entry to Viridian Postcard's Sunday Stamps - theme this week Anything You Like and next week "old or vintage stamps of your country" but as I am away again next week I have slipped a couple of this theme into this week.