What I'm thinking is the 1936 Australian aviation industry is more advanced than in reality, i.e. some of Jellicoe's advice is followed and Australia invests in building strategic capabilities in aircraft design and production (as well as shipbuilding of course). This starts with licence production of the Supermarine Seagull III and perhaps even the Supermarine Sea King single seat amphibian fighter that was related to the Sealion Schneider Trophy winner, potentially at an expanded Cockatoo Island facility which was operated by Vickers who took over Supermarine in 1926. They would also build Supermarine Southampton's, Stranaer, Seagull V / Walrus, Otter, Seagull ASR1, fighter versions of the S.4/5/6 and of course the Spitfire, then Spiteful. Cockatoo would also licence produce Napier then RR engines and a variety of Vickers types including the Vildebeest, Wellesley and Wellington.
An Australian Spitfire, even if selected in 1936/7 would take a number of years to gear up for, especially if the powers that be wanted to simplify production and improve durability. It is conceivable that the Australianised Spit could incorporate a number of improvements, such as mentioned above, and not enter service until 1941. By 41/42 it would be obvious that an improved version was needed and then maybe Australia could jump to building an Australianised Mk VIII and then instead of Griffon Spits, going straight to the Spiteful. Maybe with its inward retracting wide main gear the Aussie Spits could be seen as more suitable foundation for the Seafire and then supplied to the UK and other nations under Lend Lease.