I'm somewhat surprised at the all the just do it guys, not that I'm any welding/brazing guru, but it is a really big part and given the thin section would be big trouble if not properly preheated i.e. 500-700F and then slowly cooled. It takes a big home shop to do that safely and one that has all the stuff, big rosebud, lots of space, blankets etc. Given the size of the part and large extent of the crack and brazing needed, you'd likely have to have one guy continually heating and the man brazing will probably need radiant heat PPE. No reason you couldn't do it in the home, just that most don't have all that stuff.
I've brazed cast iron a few times successfully but its the size and thin section that make this a challenge, imo. Or am I just being a sissy about it lol?
OP, I did point you to the right place, that was who we used. I was way off on remembering the shop rate so was a bit unfair to them. Still, it was expensive ...... don't throw out those US leads quite yet. Please let us know what they say.
I also forgot, I had a small crack on my bottom panel of mine and did as Sasquatch mentions. drilled a hole,used JB weld and drilled and tapped for some small braces across the crack on the inside. It is not a stressed part, but your cracks are extensive, not sure if it would work. Is Herculock suggesting stitch or brazing? I don't think they can stitch without it showing...but maybe there is new technique.