Australia makes a quicker decision to replace HMAS Melbourne. The government goes ahead with the decision to buy an Iwo Jima class LPH in 1981/2. The government and the navy wanted to do so, but dragged their feet OTL. By 1983, the door had closed.
Edit: I would have gone for an enlarged Principe de Asturias for them, but doubt they wanted to spend the money. Could the Australians have built the ship themselves?
I wonder if a smarter move would have been the Italian Garibaldi class - the smaller of the three preferred options announced in 1979.
If a firm decision had been taken to order such a ship from the Italians to follow their own on the slips, she would have been laid down in '83 for delivery in '87. It's possible work - and the exchange of money - could have been far enough down the line for the incoming Labor government in '83 to basically let it continue.
If one could do away with the Dibb Review, and recognise the value of a ship primarily as an ASW helicopter carrier but with other capabilities, there could have been an interesting range of butterflies.
The two additional Adelaide (Perry) class frigates are no longer needed.
There would be a stronger case for acquiring new ASW helicopters earlier and more of them. Perhaps the S-70B buy could be extended to 24 aircraft, allowing for the new carrier to have a standard air group of 6-8 aircraft, with the four Adelaides carrying detachments of two aircraft each.
What was the Anzac class program may become a smaller build of four frigates - plus two for New Zealand - to replace older vessels, with the cost of eight not being justified when the Navy would also have three Perth class destroyers and four Adelaides, plus a carrier including its air group.
For a similar reason, and also in the absence of Dibb, no flirting with an offshore patrol vessel, and with only four "Anzacs" and a larger buy of Seahawks, the Seasprite saga could be avoided entirely.
Three new destroyers could have followed the "Anzacs" as Perth class replacements - in a reasonable timeframe. This could also butterfly away the upgrade of the Adelaide class, which would be replaced by another follow-on class.
Australia could have joined with Italy and Spain and acquired the AV-8B Harrier in small numbers. Perhaps 12 single-seaters and three two-seaters. This would allow for a standard air group of 6-8 aircraft in service in the mid '90s.
The carrier could have played a key role in INTERFET and then seen service in the wars on terror. She would also have been available for responding to natural disasters.
Maybe the Navy continues to win in the funding stakes, with the expensive upgrade of the air force's F-111s in the '90s shelved and the aircraft retired, possibly in favour of an extra squadron of Hornets and a greater investment in AAR - though that likely eats the savings and then some.
It all goes on and on . . .