Would the planned Light Destroyers have been built? IIRC 3 or 4 were planned but their place was taken by the 4 American built patrol frigates.
This is a very good question. I'd forgot about the DDL. Looking at the program, three were actually ordered by the McMahon Government in '72, and then cancelled by the Whitlam Government. (Whitlam did a lot of cancelling didn't he?) So if we assume that the POD makes the cost of the ships much less of a concern - and we have a more bipartisan approach to defence projects - then we could butterfly away Labor's opposition to the program, which pre-dated their election. That would mean you have three Australian-built destroyers entering service by the mid '80s instead of the FFGs. They were not light, by the way, but more general purpose destroyers, with a 5-inch gun, the Tartar/Standard missile launcher, and landing pad and hangars for two helicopters. Much better than the Oliver Hazard Perrys!
The butterflies don't end there. Suddenly you have a domestic warship building program and you're going to want to keep it going. You can follow the first three destroyers with another three to replace the Perth (Charles F Adams) Class destroyers early. Then you could move into constructing a new class of six-eight frigates to replace the River Class DDEs - basically an earlier Anzac Class program. By the time you're done there, and maybe built a couple for New Zealand too along with perhaps an AOR or LPD or two, it might be time to start building the first of a new class to replace those "DDLs" - around the mid noughties - and ironically the design could end up looking a lot like our new Hobart Class - just a decade early!
Is the purchase of the Kidd’s an option in this scenario. I seem to recall that this was offered at one point. I would expect that this purchase would mean early retirement of the Perth Class DDG’s
They were offered in the 90s iirc, but turned down due to the problems associated with Kanimbla and Manoora.
The Kidds were possibly available twice, in 1979 when the contracts were cancelled due to the Iranian revolution and again in the late 90s with the post Cold War decline of the USN. In 79 we were well along with the FFG programme and in the late 90s we were well along with the ANZACs. The timing doesn't work unless major changes of plan are made at short notice for ships not specifically designed for Australian conditions.
Riain is right - it's all about the timing. From the Australian perspective, the Kidds only make sense as a bargain-basement buy when - or close to when - they were looking to buy new ships anyway. But given you'd likely end up with a domestic warship building industry earlier, it wouldn't make a lot of political sense to take advantage of such an offer, and also one would expect with the changes posited in this thread - much more funding and more certainty of funding, plus strong bipartisan support - you would have programs in place to ensure the timely replacement of ships.