Not having a long enough easy-out, I could only have turned the lost feed-end of the screw from the head by using a left-hand bit, maybe. I'd need a sleeve to go inside the head's bolt hole or I'd risk damaging the threads trying to get a left hand bit centered? Needs to be a way to sleeve-protect a pilot bit, to hit near dead-center on the raw, jagged, hardened broken section of the bolt, like the hex section shown below. Same jagged surface on the feed-end that would need to be removed... Or else you have to remove all the bolts you already have torqued to 65 ft. lbs. and then what? You have to buy a whole new set of bolts and gaskets because you stretched them on the first torque-down and compressed the gasket(s).
When I removed the head last month to replace the bolt, the feed-end backed out easily.
This might make it possible to use a hardwood 1/4" dowel in a 90 degree attachment, depending on which bolt broke, with the drill motor switched to "reverse". The wooden dowel wouldn't tear up the threads. Any debris could be vacuumed out of the head hole later.