Very simple whiff using an available styrene kit, Flyhawk Aurora or Penelope as RAN instead of the Amphions.
Australia bought the three Amphions because the existing WWI vintage Town Class cruisers were obsolescent and in need of replacement so as to not drag down the overall capability of the British Commonwealth under existing treaties. The new Town Class were considered too expensive and (if I recall correctly) believed would take too long to build and deliver, but I do not recall any mention of the Arethusas being considered.
The Amphions were improved Leanders, the Arethusas were based on the Amphions, three 6" twins instead of four on less length. The Arethusas were considered the minimum trade protection cruisers but also proved to be excellent fleet cruisers, while being cheaper to build and operate than the Leanders, let alone the much larger Towns that were designed as counters to the large light cruisers being introduced by the US and Japan. Logically they would have been perfectly adequate for the RAN and being four of them they could maybe have replaced Adelaide as well.
Interestingly the Didos were in turn evoled from the Arethusa hull and machinery and were the more cruiser like design from the RNs Scout Cruiser studies, that also led to the large Tribal class destroyers at the lower / destroyer end of options. Australia chose to build eight Tribals (only three constructed) and a battleship (never ordered). During the war there was a plan to start building cruisers at cockatoo, with a modified Dido being the selected option, this plan continued sometime postwar.
Now for my whiff, how about Australia acquires or builds Arethusas aims to build Arethusas instead of the Tribals and the battleship, or more to the point, build Arethusas at Cockatoo and Tribals at Williamstown. This could be preceded by local construction of the two Counties, instead of wasting resourses on a seaplane carrier, from the mid / late 20s, continuously, building and maintaining a shipbuilding skills base for no extra outlay and without acquiring a useless platform (Albatross) that the navy lacked the manning for.