The Vortec heads will support more power than the stock heads. I can't really say how much. If you go with the Vortecs, you'll have to use dished pistons to get the compression ratio down low enough to use pump gas because they have a 64 cc chamber compared to the 76 cc chambers you have now. Maybe you could start another thread titled "Desktop dyno" and ask someone to plug the numbers in for you. By the way, don't be too concerned with horsepower. Torque is what moves the car.