With the iron heads, the notches are required to keep the intake valves from hitting the cylinders wall edges with any substantial lift at the valve. While the aluminum head valves have been relocated so that the intake valves will now free drop into the cylinders, the notches do still help the air flow in that area and especially when the valve lifts are increased beyond the mild performance stuff. When doing the notches, be sure that they are kept above where the top ring resides within the cylinder bore.