What's the budget? Port and polish the head, upgraded valve train with Skunk 2 cams, maybe treat the exhaust ports...on an ITR block with a knife edged oem crank will get you around 200whp using Hondata or Motec with a quality header -- but you're looking at some serious money for all that.

For the GSR block i'd look into forged rods paired up with a quality piston