Have not seen a crack in that place, but the preferred repair method would be to drill a hole at the end of the crack to stop it from continuing. That spot could probably be brazed, or you could install a series of plugs along the crack. Here's an outfit that does cast iron crack repair and sell DIY kits.
LinkThat crack isn't in a real high stress area, so once the crack is stop-drilled, you could probably use something like JB-Weld. The issue there would be to get it absolutely spotless so the crack gets sealed. That might be the best approach so you don't have to mess with refinishing the area where the u-joint ball sits.
