I am running an L28 in my 72 240z. Since the S30Z came with an L28 in North America (HLS30's) then it should not be an issue. Also the capacity increase is within the 20% increase (in displacement not power). (16%).
Technically it falls under
https://www.vicroads.vic.gov.au/registration/vehicle-modifications-and-defects/vehicle-modifications/notify-vicroads-of-changes-and-modifications
Change of engine - scenario 1
The replacement engine is identical to the original engine.
The replacement engine is an option allowed by the manufacturer for the same model vehicle.
Documents required:
if the engine is optional to the original, a signed declaration from the registered operator, motor mechanic, or dealer in that make of vehicle or an Automotive Engineer certifying the engine is optional for the vehicle model, and that all modifications made by the manufacturer for the same vehicle model with that optional engine have been completed
an original receipt for the purchase of the engine as proof of ownership of the engine
a completed Change of vehicle details form [PDF 135 Kb].
You will need to attend a VicRoads Customer Service Centre to have the vehicle's engine inspected to confirm the new engine details. No appointment is required.
Note: The optional engine must be offered in Australia by the vehicle manufacturer as an option for that vehicle (or certified variants).
And you can read more about increase in power (20% increase).
https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwiwn_myz_3UAhVLUbwKHcSeDjMQFggkMAA&url=https%3A%2F%2Fwww.vicroads.vic.gov.au%2F~%2Fmedia%2Ffiles%2Fdocuments%2Fsafety-and-road-rules%2Fvsinumber8guidetomodificationsformotorvehicles.pdf%3Fla%3Den&usg=AFQjCNFPUmsJyAtDk1qjoKMs64SgMMjJgg
I think so long as you notify Vicroads it's got an L28 in it (via Engine number) and perhaps go to the effort of getting it signed off. You should not need an engineers certificate and all that hassle. However this is not legal advice.
FWIW I've informed Vicroads and my insurance company. I'm on club rego without issue.