I'd have already welded it up. The more I look at it, the more I think the best way to solve this is to cut it off flush and then weld a boss or an AN fitting to it. The hole can be plugged when cutting it off flush so no chips get in and that isn't a problem when welding the new piece on. Cutting threads is the most likely operation to dump chips in the case, and you can skip that with a new boss or fitting.
JB weld may have its place, but this ain't it. I may be a dreamer, but you're obviously not a welder.
