Reading this article I would have to say that if I were a betting man I would make the Virginia class a strong favourite at this stage. If they are just looking at a design that requires the least modification then you would pretty much have to eliminate the Astute straight up. Not even its reactors are still in production. An OTS Virginia would match up better with Australia's requirements.ADM reports this am that a “possible” strategy for the SSN build will be for Australi to build the front half of the boats and for the US to build the stern section from the reactor aft.
Worth a thought although still speculative.
More details on Australia's intended acquisition of nuclear-powered submarines have come to light this week.www.australiandefence.com.au
That plus the Prime Minister seems to seeking advice from a committee made up exclusively with American advisors from the companies that actually build the Virginia.
Building 8 X half submarines is the equivalent of getting 4 boats built in the US so you may still have problems finding a space in their production line. Even if we just get the reactor module built OS the rest of the sub looks like something the ASC should be able to handle.