383 Broken exhaust stud please help!

First off, definitely leave the spark plugs in and stick some paper towels in the open exhaust ports while you drill. You are off center, so you're kind of screwed. Left hand drill bits and easy outs may not work at this point. I have torched out broken studs just like that quite a few times. A good tip and torch skills required, but that's what I would do. Only end studs are in water jackets, I believe.