I know a guy around my town who has done a lot of cast iron welds.
His trick is nickel rods, pre heat with a tiger torch, and hammer pean the welds while cooling.
He has even welded back together the busted to bits final drive casing off a D8 caterpillar.
The tracks were frozen to the ground, and when the half asleep operator gave it full power to try and get it to move, the final drive exploded. He welded that back together with an aircraft generator hooked up to a Wisconsin v4, and nickel rods. That thing held together for the life of the machine. Had to be atleast 40 years ago, I think it's still running strong.
It's amazing the things you can learn by hanging around with the old timers around here.
I had also learned how it was a couple of diesel mechanics at the local rock quarrie who built the first dump truck with front steering tandem axles in North America..... LOL