Get more horsepower out of a 351 Windsor engine?

If you do a lot of hwy. driving you could install hotter burning plugs,if most of your driving is city then you would want a colder spark plug. Another thing to do is remove the engine driven fan and replace it with an electric fan,that would give you about six H.P. more. Those are just a couple of inexpensive things that can be done,but there is a lot more you can do at a much greater cost and labor.