I have not watched the episode yet, but in my experience brazing cast iron is not as strong as properly welding the cast iron, and the only way to properly weld cast iron is to have an oven big enough to preheat the part and then to cool it down slow, otherwise you will make the iron brittle and it will just crack again. Even heating a block to use brazing rods will cause it to get brittle if not cooled slowly. And yes, I have tried multiple types of special welding rods. I have used nickel welding rods to fix low stress places like the bottom of a pan rail, but high stress areas around cylinders or main caps etc. I personally would never attempt, seen too many failures. Plus, a block that has been preheated and then cooled tend to shift and a lot of machine work is required to get everything back in line, just cheaper to get a different part.