If your trajectory starts back in the 60s then you don't have to be scraping in the 80s, mainly because you have 2 major events that prove the value of the carrier/ASW/amphibious ship: Vietnam and Timor. Vietnam in particular is an opportunity because the Melbourne escorted operation Hardihood which established 1 ATF and the US asked for her in 1966 and 67. Once she has been used in war its hard to argue that the RAN doesn't need a carrier, and if you have 1 then the second as a training/reserve/ASW/amphibious ship.
If you read my post you’ll see I’m starting with Labor winning the 1963 election. Calwell opposed involvement in the Vietnam War, so the economic and political cost of that - to Australia - gets butterflied away. In a cost cutting move, Labor goes with the plan of that era to operate Melbourne as an ASW only carrier - so no A-4s. HMAS Sydney would be disposed of; no conscription. Replacing Melbourne and the lack of fighters in the fleet would become political issues into the ‘70s. This is how we’d get to be involved with the “through deck cruiser” program, particularly when the Harrier comes on the scene. Obviously much more to it than that - but all starts with butterflies flapping after Menzies losing in 1963.