I've successfully Tig welded Cast Iron bases before, using Certanium Rods.
1) Heat control of both pre and post. I would put in an oven at 450-500 degrees for at least 45
minutes. Then remove and weld, then back in the oven at 400 for another 45 minutes to an hour,
then turn off the heat and let it cool on its own.
2) Stress control. I used an air impact hammer to "ratty-tat" the piece constantly. This would
remove the stresses in the iron. Take care though, if you don't pay attention to the tip of the
bit, it can cause divits in the piece that may or may not be an eye sore to look at. I have a
hammer type head that I use typically.
I would weld a bit, beat on it with the impact, and weld some more. Its not a pleasant experience
but it is effective. You can also peen it with a chipping hammer, but that gets old quick. Don't
go too fast if you stay too hot too long, or Cracking for sure will take place. About a 1/2" peen,
1/2" peen, yada-yada-yada...
If you do choose to braze, be sure to cook out all the "seasoning" in the pores of the Casting.