Long way round..sorry bear with me; as I looked through the military records for Morris, there was a signature for Bel Slack 1922. Think I am on the right lines, so in Trove there is a divorce case between Bertha (Luscombe) formerly an actress and Horace John Slack 1923
http://www.rootschat.com/links/01hog/which is as
Australia Marriage Index
Name: Horace J Slack
Spouse Name: Berta Luscombe
Marriage Date: 1901
Marriage Place: New South Wales
Registration Place: Sydney, New South Wales
Registration Year: 1901
The marriage took place on
August 29, 1901, at Phillip-street, Sydney, ac-cording to the rites of the Primitive Methodist Church. Mr. Maddocks Cohen appeared for the petitioner.
I kept looking in case the other surnames you mention came up, be glad of your thoughts