Cast iron can be reliably arc welded with almost any rod with a high nickle content. Also, any welding supply store can come up with a rod specally for cast, Ni-Rod, if I remember right. Also you can, or used to, get gas welding rod. Flux it with borax.
Always pre-heat a casting before welding to prevent warpage or cracking. Good idea to post heat it as well.
Hope this helps,
[This message has been edited by filthy (edited 10 November 1999).]