Assuming we get Battles their potential for extensive upgrades is limited. This being the case they would need to be replaced earlier rather than later. The main upgrade they would receive would be conversion three of them to radar pickets in which role they would serve until the late 60's.

 

The unconverted trio would be replaced with Super Darings during the late 50's instead of the standard Darings that were built in slow time from the late 40's. Having 6 good enough destroyers (the Battles) would have allowed Australia to delay ordering the Darings until the mid 50's when they could be built at a normal rate to an evolved design. The UK had a series of unbuilt designs based on the Daring as it evolved into the County over 15 years. These improved Darings would have had larger hulls, Seacat instead of Bofors and possibly Ikara. I know Seacat was not a very good missile but it is what the RAN would have used.

 

The radar pickets would have needed replacement by the mid 60's and this is where things could get interesting. Instead of buying, building, or modifying an existing design we could have developed our own DLG. A larger hull than County incorporating Tartar, Ikara, Type 984 and a pair of Type 901 firecontrol radars. It would have been powered by RR Olympus GT's as well as having a pair of Mk.6 4.5" guns, as well as a pair of twin 35mm GDA guns and a hanger for two Wessex helicopters. Three ships would have been completed in slow time entering service from the late 60's through to the mid 70's.

 

These ships could have received a mid life update in the early 90's including the USN's New Threat Upgrade.