There are many things you can do to increase horsepower but you have to be careful to use the correct parts so you don't end up wasting your time and money. If you are going to use the stock heads and cam than you are limeted to how big the carburator and intake you use. You will probably get all the power possible on a stock 302 with a 2 bbl. carb. If you put a carb that is too big on the engine you will just be wasteing fuel. I recommend you read the book "How to build Horsepower, Methods for building horsepower in any engine" By David Vizard. It is very imformative. I bought it Borders Books for $18.95. When it comes to building and customizing engines it is best to study as many sorces as you can get your hands on. The best methods will show up in many different places and in the long run you will have the best engine and power for the money you can afford.
NITRUOS IS NOT THE ANSWER. For nitrous
you will need forged pistons, new conecting rods and a forged crankshaft. That is $1500 in parts right there. so for horsepower on a budget nitrous is not the answer.