Carved out the huge broken crater, and destroyed threads - We had it all welded up (Thanks Dustin). Using a fire ring gasket, and an old pipe flange - we refigured where the hole would be best, leveled it out, tilted the drill press table, and drilled and tapped for 5/16-18 USS. I like to use a stud. Mount the exhaust pipes with NO STRESS on the head pipes. They almost stay on and seal with no nut, then you know there's no binding. The pipes are clamped to the frame and brackets, and square and true (no binding) at the heads. Only then, I tighten the head/flange fully.