Fella's ease up a bit don't be so hard on the new guy just takes 2min to give him a modlist and be on your way. Besides although a very good guide to 300hp it could use a little update (may have already been updated haven't been in it for about 2-3 years).
Anywho, to the OP. 300hp isnt very hard. simple bolt on's and a decent tune will get you there.
With a high spike in boost you can easily make 300hp. However you will only be making 300hp for that split second. The key is having a nice power cure. A car making 280-270hp across the power band will smoke any other car making 300hp for a split second and having the power fall off to 230-250 at redline.
You can have the best of both worlds though (magical 300 number and decent power curve) with the mods below and a good tune.
3in turbo back exhaust (or a e-cut out dump if your strapped for funds)
Ported intake manifold
Ported stock throttle body or larger aftermarket throttle body
Cold side hard pipe with external BOV and BOP for the stock surge valve
Walboro fuel pump
You can get by without a few things that are on the list but that will get you the power out of the car that you are looking for reliably and safely.
Note: Depending on the history of the car other things may be needed for the car to handle the power above (example: clutch, motormounts, plugs, wires, etc)
Rage-tek can get you anything you need and help you make your goals a reality.