I sell semi-custom intakes to people almost everyday who are making 400-500+whp on street cars. Some of them drive these cars daily. It is doable, but the before-mentioned points about the cost and reliability are valid. *If* your goal is 450whp, here is what I would do to shave some cost off your build.
-The stock-mount GT35R and the supporting mods will make close to 450whp on 91octane at sea level. It will be laggy up here near 5k', so plan on keep your revs >4krpm for any boost.
-Do the stock shortblock with forged pistons. The improved bearings and studs are a good idea too. I think you could get by with the stock rods (on a street car), but that is a judgment call.
- Instead of the very-expensive Cozzy heads just do stock heads with maybe cams, and maybe 1mm-over valves. My buddy Ray has pro-ported STI heads with oversized valves if you are interested though.
- Get a good conservative tune by somebody with lots of experience tuning street cars in the 450+whp range.
- You will need a new clutch with this build or your dyno-tune session will be cut short.
That shortblock will not last forever obviously, but it is enough to get you into the game for a year or two... maybe. I don't think you need head porting, but it would maybe help you make the power at a lower boost.
Also please check with me on any parts you may need. I have good wholesale connections on shortblocks, pistons, rods, cams, gaskets, oil pumps, etc. (click for list)