I was under the assumption that you couldn't put an engine from an old car into a new car? Regardless od them both being buick engines.
Im not sure about the laws in Vic related to this, but in Qld they dont allow an engine from an older car to be transplanted into a newer model. This could also make your wifes car unroadworthy.
If you decide to go with it you may well breach roadworthy laws and if you had an insurance claim it would not be paid as your engine setup does not comply with that model car. Your car is deemed to be unroadworthy and unregistered in this situation (in Qld it is)
If you went the other way and used an engine from a newer car into your wifes VP, there would be far less hassles with roadworthy rego and insurance.
Check your state laws, go online and google search it, or let your fingers do the walking in Yellow Pages.
The info will be there, keep digging and it will surface.
Its wont be too hard to find
Good luck with the transplant