I'm a professional welder. I have learn the techniques to weld cast iron with smaw and oaw.
I'm agree with ciladog but you have to pre-heat and keep the welding zone hot during all the process (beetween each pass) and tempered down very slowly with
some refractory material like. 50 celsius degrees on 1 hours to optimized the weld link.
If your not sure to do it, ask a professional welder, but don't expect him about some guarantees about the solidity of the work.
Because the cast iron is not destinated to be welded, it's only a repair and it's never done a good fusion beetween the rod material (smaw= ni-rod).
In time it will be crack again near to the link zone. Yes you don't have lot to lose in trying.