My guess.... $585,000 plus the buyers premium.
Close...
UPDATE, 25 May 2021: Sold!
The 1985 HDT VK SS Group A has ended with a final auction bid of
$1,057,509 (with 7.5 per cent buyers premium of $79,313 on top), making it the most expensive Australian road-car sold. The winning bid was made, 26 minutes before the auction ended, by A. P. of Strathmore in Victoria.