Nobody here has ever successfully put an A15 crank into an A12 or 1200 block & made it run.

The A14 crank conversion, however, is not particularly difficult.

Im interested in the rule about not being permitted to drive a car with a mod plate. This means that if a car has suspension, steering & brake system improvements as well as other safety related changes, all of which are approved, your girlfriend can't drive it, even if it still runs a stock engine.

Yep, it must be Queensland.

The original 1200 gearbox is a 56 series while the 120Y gearbox is a 56A series. This means that the internals were strengthened a little but the parent manufacturer still did not use it behind even an A14 engine for good reason.
Have a think about why this is so.