VL - rb20det upgrades

Hi there i have a VL Commodore with a rb20det in it just posting to see what else i could do to the engine to increase power but for as cheap as possible and ideas??? Bolt in's would b good SPECS--- - Rb20det rebuilt 7000kz ago - Wasted spark setup - GFB Boost tap (running 12 psi) - 500hp walbro fuel pump -rb25det turbo - b.o.v -2 and half inch straight through exhaust from the turbo -Performance front mount intercooler.