[Raptor]

If you are careful with the tap and drill, it can be done and you are right, JB weld is pretty ghetto. There are metalic composites out there that can be used such as Devcon that are considerably better than JBweld. In fact some of these are used for casting repair and titanium repair and machinable afterward. But as Josh mentioned, you can tap the head just fine. It isn't a mysterious black hole, the galleys are accessable and the chips can be removed.