Ive seen a few threads about broken bolts and advice on removing them. There is always a old school trick to removing them which may or may not lead to success. If all of those methods fail and you have to resort to drilling that bolt out that is when things really start to suck. I wanted to recommend a tool I have used on diesel engines for a few years. They have a template that bolts up to the head and uses guides to help you drill a perfectly straight hole. Most of the time you could do this on the vehicle without having to remove the head and send it out or do it on the bench. I recently have seen them expanding on their template kits offering multiple engines in all makes. What caught my eye was the universal kit that would be useful for other engines, water pumps intakes etc. Anything you could get it mounted up on. Its not exactly cheap and may not be something you can justify spending money on for one bolt but its one of those tools that your glad to have when you need it.
I have a couple of the very early templates when they first started making these. These guys are a down to earth company and customer service is great. If you can justify it they are worth the cash. I plan to pick up a universal kit too keep in my toolbox
https://maniboltdriller.com/product/universal-drill-guide-system/