Okay, I just spoke to the NSW RTA and they said it's not a problem, 'cos as you guys have pointed out, the Compliance Document specifies the VIN and engine numbers and there is no wucken furries.
Cool, now I can get my new plates.
Mind you, I feel a little dubious. After having the same plates since 1982 on the car, I'm hoping it's not bad luck to change them (yanno, sorta like the superstitous bad luck when you change the name of a ship).