Coolant leak -hydro locked engine

I wouldn't use epoxy on anything practically, because JB weld flows about the same and is WAY tougher.

I know it don't mean squat overall because it's just another a-hole with an opinion :D
But this is what I would do if it were my head and I was trying to save it.
First I would chip any loose material off in and around that hole and get it down to solid material.
Then I would use a small piece of plastic coffee can lid on a stem of some sort so I could push it through the hole but still have ahold of it behind the hole.
Then I would flush it with Muriatic acid, then water and blow it dry.

While holding the plastic "backing" in place I would inject about a teaspoon of the slow set JB weld into the hole.
THEN, I would stand that head so the hole was directly under the JB weld so it could lay down and solidify over it inside the water jacket.
Once it set up for 24 hrs I would go back and grind down the stem that held the plastic backer and refill that dibbit with JB

I would watch it close after, but I'll bet that would do it.

(Like I said, just another opinion) but based on knowing my adhesives and sealers more than most I believe.

On that note, I have successfully welded some pretty sketchy stuff, and I don't think I would even try that on it.
Attempting a weld right there with how thin it must be in that area, a waste of time IMO.
Probably just instantly blow a much bigger hole in it.