Got this info off Ls1 site..
Street Tuna from Adelaide has finished a variety of low to medium boost turbo upgrades as well as a s/c kit for the Boss 5.4!
The turbo on low boost (10-psi) has 260rwkw!!
Link->
http://www.capa.com.au/main.htm
Upgrades will be sold and fitted through authorised CAPA dealers