rods/pistons, and maybe some ARP head studs and main studs if you want to do it right. If you want to push more than 12 PSI, a block guard would be a good idea. So would a good set of cams and valve springs so you can spin the motor nice and high, but you don't have to. Top it off with DSM injectors (or some good 550cc) injectors and a Apexi S-AFC and you're in business. You won't need 550's unless you plan to run some serious boost. DSM 450's would be fine for 8 PSI and most of the turbos that are efficient under 14 PSI or 500 cfm.

You'll have to hack your exhaust or replace it altogether, but it's worth it. Whether you go for internals or a turbo, plan to spend at least $2500 if you want to impress the ol' butt-dyno. You'll have to replace all the stuff I mentioned going either route, except maybe the injectors... but you'll still need fuel control with a built NA motor.