[John]

I would still try to mig weld a nut over the stud. Weld a flat washer to the stud first then weld a nut to the washer. When done carefully and slowly, the weld will not damage the threads in the cast iron. The heat on the stud will help to free it up. Do not try an "easyout" because if the stud broke off due to being seized in the threads, the "easyout" will probably break off too and then you have a real mess.