I'd go w/ the 9.5:1 personally. It'll help you have a bit more low end and spool quicker, and it shouldn't present a problem w/ the power levels you are aiming for. It'll just make for a more fun street car.
I think you'll probably be fine w/ 3.73's, but remember that you don't need a lot of gear w/ a turbo setup.
Ported PI heads, crower cams, and a good shortblock should easily support 500-600. An extrude honed Bullitt Intake or Trick Flow manifold would be ideal...maybe even one of the P-51's (I have never seen one in person lol), but a PI intake would probably do the job