Remove the manifold piece with what's left of the output flange on it, and have a machinist fabricate a flange from steel, not cast iron. Then mill the remaining ear off the manifold and weld the steel flange onto it. Welding steel to cast iron is tricky, but it's doable. You'll need to find an oldtimer who knows how to use nickel-alloy welding rod, preheat, weld, post-heat, peen, and slow cool the weld in a pile of sand to prevent the weld from cracking. Once a few passes of nickel rod are in place, you can build up a thicker weld bead with 6011, 7014, or some other general purpose steel rod. The mild steel welding rod will bond to the nickel alloy without concerns for cracking, as long as it doesn't overlap onto the cast iron. I learned that trick from an oldtime welder/pipefitter when I was a maintenamce man at E&J Gallo winery, back in the late 1970's.
Jerry
