i did some research on this when my car got its engine swap.
RTA NSW said on their website that an engine which is not larger in capacity by more than 10% (i think) is classified as owner certified, not requiring engineering signatory. when the engine size surpasses this quota, engineering cert. is required.
my car was "owner certified" but that didnt stop the prick of a cop giving me a defect 12 hrs afetr the motor went in.
do a search for "guide to light vehicle modification" it will tell you everything you need to know, its an RTA website.