I have a 66 cuda put in a 340..... I can tell you straight up there are no manifolds available that will fit AND that you will be happy with. TTI makes headers as does hooker and one other that I cannot remember.... TTI's are about the best but they do require some modifications ( not easy) absolutly forget Harold & spitfires, waste of time and energy..... the pissing thru a cocktail straw is about the best one I have heard so far...... TTI's are around 900 custom built like mine are a bit more but NO mods necessary and they are built to the car....meaning changing plugs and OIL is no biggy
good luck