Making power out of the 318

A 400hp 318 is definately doable, but not for 3 grand. Not sure what machine shop rates are like in the US but over here you would spend most of your budget just on machining and balancing.
I will go against the grain here and say a 15/16 year old in car built in the 70s with a 400hp motor is a recipe for a written off car or worse. (I daily a car with 400rwhp and if I had this when I first got my licence I would have probably killed/seriously injured myself and others). 99% of people your age wouldn't know 400hp if it slapped them in the face.
My advice would be to spend that money on making sure your brakes & suspension are in top condition and a good set of tires. Drive it with the slant for a while to get used to how the car handles and reacts to different driving conditions while saving up and planning for a higher hp motor down the track.