Cylinder head repair ?

[sleepertruck72]

So at work I had to pull the driver side head to attempt to remove a broken exhaust manifold bolt... The bolt at the very rear of the head.. #7 cyl. So I get the head out and try to get the broken bolt out using Snap on screw extractors...No luck. I didn't take an after pic but its not pretty. The drill bit went kinda sideways. My question is : How big a helicoil can I put in to finish this without damaging the head or hitting water jackets ?