If your building an want big boost go low compresion forged internals, $$$ though. I dunno about the head problem Gorn mentions but you'll need some better ones anyway and fully hardened valve train. A 8:1 comp ratio should see 12 psi, with a really good tune. My pals skyline gts-t was 9:1 comp ratio and ran 10psi, and was max on engine to run 14psi, but turbo would hold it. If you run stock compression id only go 5psi max!

Take your time do it right, get the right parts and you'll have a good motor. However I would prob start with a 3.8 V6 if you could.