The bolt pattern on the manifold is "4 center to center, "2 1/4 diameter pipe, gasket hole is "2 1/2. looks like extruded metal with gasket impregnated into it. pipes were fabricated by a muffler shop using a coded bendind machine. I even tried putting an exhaust doughnut in side with the gasket and it blows out.checked mufflers and pipes for restriction, both are straight through. I think I remember seeing a double cone doughnut somewhere but have not located one yet. Thanks for your quick response.