If I remember right, the 4G63 Starions over there are all SOHC, right? Are they the same 4G63's that are in the EVO series for you guys? From the sounds of it, the Aussie Starion 4G63 is completely different than what we have. Our 4G63's are like what is in the Galant VR4 and EVO series. It sounds like your 4G63 is little more than a G63B for us...which was put in our Mighty Max.
Regardless of that fact, the 4G63 powered Starions over here (using the DOHC cylinder head) are all performing very well. A few starions running 4G63's are running 9 and 10 second 1/4 miles.
There are a multitude of 9 second 4G63 powered DSM's and even a few 8 second 4G63 powered DSM's. a JDM EVO VI came with roughly 320hp (although, on paper, they're limited to 270hp). With little more than a boost controller, exhaust, intake, and proper tuning, it's not uncommon to see a 3200lb DSM running 13.xx's.
Now, granted, a 4G63 will not have the low and mid range torque as an L28, but, if you build the stroker 4G64/4G63 hybrid, you will have L28 type torque, but still have high horsepower capabilities. It all really comes down to the L28 head design not being overly horsepower friendly.