A quick look at the victorian Vehicle Standards Information (Sheet 8 - Guide to Modifications for Motor Vehicles) in relation to Engine Modifiations states;
Replacement Engines
Where it is intended to fit an engine which is significantly different from that offered by the manufacturer as original or as an option (e.g. four to six cylinder or six to eight cylinder), then an Approval Certificate is required as evidence that the vehicle in its modified form is safe and meets all the applicable construction and emission regulations for that model. It is recommended that a VASS signatory is consulted before commencement of this type of modification.
I have also spoken to several Engineers and the opinion varies greatly.
Some say, no I cannot do this mod with this Engine/vehicle.
Others say, yes, but I must put it on Gas.
And others say, sure, go ahead and bring it in when done for a certificate.
No prizes for guessing who is getting my work :lol: