Tube steel headers are notorious for warping the flanges where they attach to the cylinder head, and blowing out gaskets. They also raise the underhood temperature by a huge amount because the pipes ahead of the firewall are so thin, and a lot of that heat finds its way into the cab, after melting wires, etc. Cast iron split manifolds keep the heat under control better and unless the bolts get loose, they don't blow gaskets. The 120-degree separation of exhaust pulses also helps scavenge the cylinders better than the stock exhaust and marginally increases torque.
Jerry
