I've had many cast iron motor parts repaired, both with cast iron welding and stitch(and lock) repairs The BB 906 heads had a bad history of cracking under the center exhaust ports, especially if left to freeze with water in them I know several BB Mopar racers who would drain the block and radiator and not use anti freeze in the winter to flush the water out of the heads in the high Desert of SO CA, both had heads frozen and broke the next year Same thing on inboard boats up there and motor homes plumbing