There are places that'll sell you everything as a kit, I've been looking at the various stage 3 kits at about £2000, factor in another £350 for 440cc Bosch injectors and it looks like 350bhp is accessible. Although beyond this my engine would need forged internals so a personal preference is to either remove my current engine, rebuild and fit stage 3 or buy a CDL engine and place that in instead of my.current engine.