Can I run the 9PSI boost pulley upgrade kit to suit Holden L67 in the completely factory engine?

It would depend on the fuel you run on a consistent basis. If you run on 95 octane fuel then the highest we would recommend would be a 8 psi pulley kit, 98 octane fuel a 10 psi pulley kit. If you wanted to be conservative and ran 98 octane fuel, then we would recommend a 9 psi pulley kit.