Being a GM approved (or whatever) supplier, Callaway was contracted to build the top-of-the-range 300kW (400 horse) LS1 that is used in the Aussie and New Zealand HSV GTS sedan and coupe. Without going into specifics, CW machine-ports the heads and installs a different cam. These engines are shipped to Aus and are factory-installed into 'core' cars that are destined to become HSVs. You may not be able to get the exact HSV bits (the IP belongs to HSV), but I'm sure Callaway could be able to do something for you!