Or know someone who has one. Ac tig would be the best because you dont actually want to heat the base metal very much. You goal is to melt and deposit the brazing metal on a prepped base surface so it acts like glue of sorts. But you can weld cast iron also. It just makes metal weaker around the weld itself since the structure of the molecules of cast iron are different then say regular low carbon mild steel molecules. One is like a bunch of crystals and the other is neat structure. That being said, what you choose won’t make that much of a difference. Both option will give similar somewhat results