Just got this reply (at last) from VicRoads
Thank you for your reply email. My name is Lee and I am able to assist you.
We need to confirm the following information:
. is the vehicle registered in your home country
. are you visiting on a temporary basis.
If so, it can be driven in Australia if it meets all of the above conditions. Also, it must have appropriate transport accident cover. By having coverage in NSW, you should be fine to drive in Victoria during your stay.
I hope this information is helpful to you.
If you do have any further questions, please do not hesitate to email us back through the link
Feedback & enquiries : VicRoads, providing your email reference 500669881. We will then aim to respond within seven working days.
Alternatively, you may contact the VicRoads Call Centre from overseas on 03 8391 3216 (8.30am - 5.00pm Monday to Friday, 8.30am - 2.00pm Saturday AEST), to discuss your enquiry further with a VicRoads consultant.
Kind regards
Lee
Customer Resolution Team
VicRoads Contact Centre
I asked if an overseas registered vehicle arriving from overseas in NSW on a Carnet de Passage would be allowed to travel in Victoria using the NSW third party arrangements and gave the weblink to
Visiting overseas vehicle < Get a new rego < Registration < Roads and Maritime Services