Having read all the praises of NI-ROD (nickel welding rod), I have it
from an owner of a welding shop, and good friend, that welding cast
iron with NI-ROD is by no means a sure fix.  NI-ROD on cast iron is a
cheap but not a conclusive repair.  You run a considerable risk that
another crack will open up next to the weld.

If the item is cheap, you simply replace it, if the weld fails.  If you
are welding an irreplaceable 1930 Deusenburg engine block, you use a
cooling furnace, a gas torch and cast iron rod.  Needless to say, it is
costly.  I have had an irreplaceable item welded by an expert.  The
repair was permanent and the weld was indistinguishable from the rest
of the metal.  While I was at the shop of the person who did the re-
pair, he showed me a large part from a rare racecar.  It had been
cracked into three pieces.  He challenged me to find the welds.  I
could not.

Larry Mayo.