[BCreekDave]

The only alternative I can suggest is brazing the crack. Braze, while not as strong as weld, is pretty forgiving for cracks on cast iron since when the cast iron cools it will "stretch" to the surrounding shrinking iron rather than pulling the iron. You can ceramic coat it afterward to cast iron color (I've had good luck with Cerakoat Glacier). I've seen punch press frames brazed together that have lasted for years afterward. The manifold would be much less stress than that. Typical heat on the manifold is less than the melt point of braze. Maybe worth a try.