You got to be careful what length bolt you stick in there. Maybe somebody forced the wrong length or wrong diameter or tried metric.
That bolt doesn't really need to hold much. I'd JB weld a stud in there and not over tighten the nut.
A trick to using JB weld, is to coat anything you don't want stuck with car wax (or oil). If you pick your time right, you can get the excess JB weld off of there fairly easy. It cures from sticky, to crumbly, to hard. It comes off pretty easy if you catch it between sticky and hard.
I'd try to figure out if the crack goes all the way through to the water jacket.
I'd use a light coat of silicon on the gasket.
Getting JB weld to hold well is usually in the prep, clean it up well, multiple times. Scratch it, wire brush or whatever it taks to get it clean.
With good prep. I've repaired radiators with JB weld, that held five years.
Another solution, would be to drill and tap for the next bigger size and then use a stud and JB weld.
