If you have a 1971 it technically will need to meet the appropriate adr requirements. I’m not sure how strict they are in Vic?
Looking at VicRoads it says:
https://www.vicroads.vic.gov.au/registr ... cing-seatsQuote:
Replacing seats
A VASS Approval Certificate is not required for a replacement seat provided:
-the seat is offered by the manufacturer as an option and is replacing an existing seat
-the original seat mountings are used
-appropriate seatbelts are fitted.
A VASS Approval Certificate is required if:
-the replacement seat was not offered by the manufacturer as an option
-the vehicle was manufactured on or after 1 January 1969.
If an approval certificate is required, you will need to advise VicRoads of this change.