Well, I hate to burst your bubble, but your chances are slim at reaching 300hp (crank or wheel?). Unless you plan to spend $1500+ on it, and that price doesn't even include a mandatory trans rebuild with a shift kit and hard internal parts. Other than that, the trans will be toast, as it cannot handle gobs of low end power in stock form.
Also you need to start small, such as a full tune up, the car needs to be in perfect running condition before even considering mods. The exhaust manifolds on these are known to be some of the freest flowing manifolds GM ever made, but they do have a downfall, they like to crack due to age. These and many other things are what you have to start with before considering modifications.