Question: Is your car a private import?
Before you go any further read the government regulations, here:
http://www.getrouted.com.au/documents/DOTARSRegsVSB10_07.pdfTo quote: "Vehicles built before 1 January 1989 may be imported to Australia without restriction.
An import approval is still required and the enclosed application from should be used."
To answer a couple of your early questions, while Mini production in Australia ceased in October 1978, there was still stock at the factory and in dealerships and cars were being sold well into 1979 - at least to May. Compliance plates were fitted, and dated, when the cars were sold to the dealerships and I have seen and heard of compliance plates dated up to April 1979.
No Australian-built Minis had anti-intrusion bars in the doors.
If your Mini is a 1979 English-built car, then you should not have to meet the current ADR requirements. Oz Mini Cooper is the only place in Australia, as far as I know, that is certified to comply post-1995 Minis, but read the DOTARS regs thoroughly to determine what is required for a 1979 car.
Cheers,
Watto.