What kind of power are you looking to make when you go boost? Also, what size turbo are you planning on running? 250whp-300whp you can just run a stock gsr. 300-400whp you can do a rods and pistons gsr. I don't see a big gain in using the B16 head if you plan on boosting later. I would put that money towards a good turbo and tuning. You don't have to do valves and springs and retainers unless you plan on running high rpms (above 8500) or run big cams (not needed for <400whp). As for what pistons to run I would personally run a 10:1 JE and get the car tuned. This will make the car a little more responsive when out of boost and you won't have to run as much boost to make good power.