Only way for a hobbyist could weld a crack that big would be to weld one, 1/16" dot at a time with one day in between each weld.
If you try to run a bead on room temperature cast iron, you will get spider cracks running in all directions. If you don't have an oven to put it in right after you weld it to allow for slow, gradual cooling, the weld bead will likely crack.
