It looks like some kind of repair or cover up has been done previously in the one picture. What ever that material is on the surface would have to be thoroughly ground off to do any form of welding. To do it properly with someting that thick you need to remove the entire part, and grind a v-groove to get full welding depth, then with nickel rod for cast iron you need to pre-heat the parts and make short beads, peening immediately after each bead to relieve stress. Then that hole in the part will have to be re-machined.
Then you are still at the mercy of the quality of the casting and its impurities. So like another person said find out about the replacement cost and availability.