We (Beck) are just finishing our prototype chassis specifically designed for ADR approval and working with a company in Australia to meet ADR and get a certification number. We did this with our Spyder many, many years ago, and as far as I know we are the only P-car replica company every to get true ADR approval. I know I've seen several companies say they were approved for Australia but when asked to provide the ADR approval number the conversation ended... Unfortunately that version of the 550S with inline VW motor is no longer available, so that is a moot point at this time, but it was done in the past and can be done again.
Anyway, it'll still be several months, but due to the latest round of ADR rule changes, I believe this will be your only option for a new build. I know there are some loopholes for an "old-timer" that has been not he road for 25 years or more, but even then, it is my understanding that they will no longer allow shortened belly pans.