Rhyming slang isn't really new - for example "Partridge's Dictionary of Slang" gives ROUND THE HOUSES for Trousers, quoted by Augustus Mayhew in 1857. If rhyming slang was current in London at that time, it'd not be surprising if it cropped up in Australia.

Not that I'm contesting your suggestion for Matilda, Bob, which sounds plausible.

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The "Who'll be a soldier for Marlborough" version I've always understood was made up by Pete Coe. If there's evidence for a Second World War sighting of it, it'd be interesting.