Whenever I am using cast iron intakes and heads, I have never had to use the fiber gaskets with the valley pan. However, when using aluminum, I have always used the fiber gaskets to sandwich the valley pan. I bought a vehicle several years back, that had a 440. The guy I bought it from had installed a TM-7 intake and didn't use the fiber gaskets. After 100 miles of freeway driving, it developed a nasty vacuum leak around the intake and left me sitting in Friday rush hour traffic, Christmas weekend in Portland, Oregon. It was not one of my happiest afternoons.