I recommend you check into a set of March Performance Power & Amp pulleys... this kit comes with an overdrive pulley for the alternator, and they advertise 10HP to the rear wheels. The billet aluminum ones are the nicest set of pulleys I've ever seen, but they are pricey compared to the steel (heavy) pulley kits. If you got the dough, get billet aluminum...
rule of thumb... less rotating mass = more power