Sonny,
If you can take a little suggestion on welding cast iron, don't use NI rod!!!!! Tig it with stainless filler wire. I have been welding castings for 30 years, and never had one break. Clean it with grinder and use root pass and filler pass, then if you like, a cap pass making sure you "tie it in on both sides" if you want to make it extra strong (you say you are machinist) cut a groove across the weld and put a piece of keystock in it and screw it in, then tig it with stainless. Never will let go again as the key stock is soft and will give and still hold.
I am toolmaker of 45 years also and have my own shop here in basement.
Just my $0.02 worth.
Frank