Yes i have been quietly wondering about this as well, in a previous life i was a Subaru enthusiast and converted an L series wagon drive train to an RX turbo setup and I did the same with a 92 Liberty GX wagon and did a full RS Legacy swap into that compete with a stolen generation WRX turbo setup and self modified STI exhaust. the conversions were within the approved mod rules as they were the same as available factory and the official output of no more than 20%. This was in the 90's and the rules were a little more freed up and blue slip certification was a bit easier to get done.
However googling it and looking at the 2013 light vehicle modifications for NSW, it does state for the engine - examples requiring certification - Fitting a turbocharger/supercharger to any vehicle of a make and model not offered with a turbocharger/supercharger by the manufacturer. My argument there is that it was offered in overseas markets with the same turbo setup and it was fitted to other Volvo models released in Australia, however it is a fine line to draw in the sand.
So interestingly I am looking down the path of bolting in a 740 turbo engine setup into my 89 wagon at some point (once my stupid course is complete and I get two 240 sedans roadworthy) and yes this time around i will be looking at trying to be somewhat more rule compliant as well.
