As you can see from these responses Daz, there is no definitive answer.
 
Like I said in my first post, call your local registry or call an certified engineer in WA.

Thats right, I really only remember the hood ornament , hence D-cups, lol

http://www.mr2australia.com/default.asp

i fink the search functions still work

The only way I can see being able to fill the guards legally is offset.
RE: different factory spec'd cars: if it's a genuine change within that model of car that comes with larger wheels...this should have a factory plaque stating the wheels' dimensions for this particular model. So if it came with 19" from the factory - 21" would be a legal choice, provided this complies with the concerning state's laws.
There was discussion raised on the old forum to run JDM spec Supra plaques on our cars - as these came out with 17's all round yes? I wouldn't suspect there would be too many Japanese reading cops around. Unsure if the RTA have manuals with factory specs for each car/model for them to be able to tell.

List of ADRs are here:
 
http://www.infrastructure...design/adr_online.aspx

Lads - all good input;  I have compiled a list/spreadhseet with some surprising results - and track is basically the limiting factor;  So it works a little something like this, though I will be putting a full formal list to the thread when I get home form work:
 
1. Rim width for an MR2 is legally allowed to be up to 11" and the maximum tyre width is 285 at the rears, based upon a table published in VSB14 Section LS - Tyres, Rims, Suspension and Steering.  BUT this arrangement would not comply with other areas of VSB14, most notably the rolling diameter clause, which cannot increase over OEM by more than 15mm.  In the case of using a 19" x 10.5" rim (for example only), this size exceeds the rolling diameter limits by over 50mm.  Therefore to be acceptable to the authorities, they would have to be "certified" by an approved engineer, even though they are within the the max rim widths and tyre sizes acceptable in the published Table.
 
Interestingly, the term "acceptable" in this case means a certification or permit is NOT required.  That does not necessarily preclude you from going down the path of your own choice of wheels, as the VSB14 documentation states that the VSB's are there to assist car modifiers, though if you were pulled over, the rims were defected and you hadn't had the wheels specifically certified as a modfication and approved by the authorities, then they are considered illegal. 
 
2. The term "engineered" means approaching one of the published list of the WA consulting engineers and obtaining a certificate for submission to the authorities for official recognition and documnetation that the wheels are safe, and do not contravene any other part of VSB14 or the ADR's.  This certificate becomes a legal document for that vehicle and must remain with the vehicle, and passed on to any new owner.
 
That said, the track increase then becomes the limiting factor - even if I could get through an engineering cert for a set of 19"s with increased (over maximum "acceptable") rolling diameter, arty is correct in a tracking increase of 25mm is maximum acceptable.  This equates to a change of offset of no more than 12.5mm each side.  Now, I don
t know the poriginal offsets for stock rims, but I'd say a few of us may be close (without knowing it) on our 16"s and 17"s...
 
Gotta get back to work now, but a full response is coming, as I feel I have adecent handle on it now:  If anyone can supply the original OEM offsets this will clear up the tracking issue for everyone...