urban humour flashback

Whitebait just read of an amusing joke which circulated round the late 1970s/early 1980s--presumably originating from Sydney--that editor Jim Davison mentions in his introduction to The Sydney-Melbourne Book (1986).

The joke identifies what a group of three people would be identified as in the respective state capital cities -- a deputation in Perth, a quorum in Melbourne, an illegal march in Brisbane, relatives in Hobart, and a thoroughly modern marriage in Adelaide.

(A bit of historical knowledge of the Australian political landscape of the time is required here--except for the Hobart crack. Can anyone explain the drift of the Perth reference to Whitebait?)