The plate is genuine New Zealand and indicates that the van was assembled there. You can just see the "NZ" after the S.
I've been trying to come up with some logic for this.
Maybe the van was built in Sydney as a complete standard van and then sent to the New Zealand Holden assembly plant where it was fitted out as an ambulance and the original body plate was removed and replaced with this one. I think the NZ plant only routinely assembled sedans during the FE model run
The old trim and paint codes would have been wrong since the van was retrimmed and repainted. So the easiest thing to do was replace the tag and stamp the new one with the original Sydney number - This is only a theory