So the bolt is broken in the iron cylinder head? With a 1/4 inch showing you are in luck.
Get heat on it from an oxy-acetylene torch. Get the bolt absolutely red hot. If the surrounding cast gets red that's OK too. Even better. Allow to slow cool.
File two flats on the side of the bolt sticking out - use a lathe file that has no teeth on the edges. Just small flats. Then get a good sized ball peen hammer and give the top of the bolt a sharp, well-aimed hit, which may be tough as it's horizontal.
If you are keen on penetrating oil, now is the time. Or not.
Then clamp the vise grips on the flats, and it should just spin out.
Whatever you do, don't attempt the job without lots of heat first. If you mangle the stud, or snap it flush, you'll be pulling the head or the rad and rad support ( assuming it's a 240/300 engine)
Good luck. Stay calm.