The above advice you have been given is good. However the rules can vary from state to state depending on the situation.
The document the states and territories refer to is VSB14, with a link below.
https://www.infrastructure.gov.au/in...bulletins/ncop
Read the first page (and only) carefully from top to bottom. The only thing you need to read from the Documents section is NCOP03 which has a link to a .pdf to click on.
This will take you to the engine section which has an index on the 4th page. Section 3 will refer you to page 13 which gives you a rough overview of what you may need to do.
You have not specified what engine you are fitting to what vehicle. This is where you need to seek the services of an engineer approved by your registration authority to guide you further.
Unfortunately this system is in reality a rolled gold shining turd of government ineptitude at both Federal and especially some State levels. It is difficult to navigate, confusing and can be costly for enthusiasts to use.
It is important to seek information only from capable people who have direct current experience with your local system.
Best of luck.
A much better system can be found in NZ.