I assume you're talking about a 351C here. Yes, you need the valley pan, otherwise the oil splashing on the bottom of the intake where the exhaust cross over is, will cook, crud up and make a mess, also increasing oil consumption. Now, if you block the exhaust cross over or use an aftermarket intake that has no cross over, you don't really need the valley pan. You can also use the valley pan with composite gaskets by cutting the gasket portion off the pan and setting the pan down into the valley before installing the composite gaskets and intake.