383 Broken exhaust stud please help!

The drilling, tapping, or ez-out stuff never works. Heat is the only way.

If it were me, I'd pull the head and place a nut over the broken stud and fill with weld from the stud to the top of the nut. The heat from welding is usually enough to get the stud moving. There's usually a lot of corrosion on the water jacket side of the threads, so may need to loosen/tighten several times while adding more heat and blaster.

I did have a machine shop mill one out and thread oversize once, I ended up have to use a stepped stud but it was a good repair.