Good luck with this.
A few years ago, I discovered that I had been illegally towing, among other things, my Goldstream Wing1 with my '93 'Cruiser ute. The ute has an official tow ball rating of only 112kg, even with a 350kg Hayman Reece tow bar
In '96, the same vehicle was rated at 250 kg ball weight. I contacted QLD transport, via RACQ and had a really good group discussion with some department engineers, who were openly flummoxed by the rating from Toyota.
Because it was the manufacturer's rating, there was nix the engineers could do about it, except offer sympathy. They said that Toyota could, perhaps, release a statement re-assessing the tow ball rating.
On contacting Toyota Australia, there was a decided lack of interest, on their part.