I'm gunna disagree with you there. Having recently looked into this myself I found the current rules from the dept of transport website, then spoke to a QLD based engineer.
50mm larger is all you can go on diameter of tyres, and 50mm is all you can lift in springs, neither of which require an engineer certificate.
You can do a further 50mm body lift however this will require an engineer certificate. It is however pretty pointless, as you can already fit the legal limit of tyre size without a body lift.

