The Felpro is not made by Detroit,both are made by Corteco I guess, maybe to different specs. The UPS guy just dropped off the Felpro 261 gasket,it's coated with the blue stuff,looks like the Detroit gasket that is coated with black stuff, except the Felpro sealing rings around the cylinders look better.i get my burley neighbor to help me with the head and that's the end of this story,lol.