Removing Head Bolt

Ok I am removing the crappy smog heads on my engine. I have a question regarding the removal of the bolt at the back of the head over the #7 Cylinder on the drivers side. (Last one towards the firewall) I cannot get any of my 3/4" sockets over this bolt squarely to break it loose. I have tried several different sockets including 3/8" and 1/2" sockets and all of my metric sockets both 12 pt and 6 pt. Is there any other way to get around this bolt? It seems as though the casting on the head where the top of the bolt meets the head is too narrow to get the socket to set in tight. Do I need to remove the valve spring to get at this bolt? This is getting really frustrating.

Just looked down directly at the head, it looks like there is some type of slag or something, almost like a weld slag, round and about 3/8" near the bolt which is preventing me from getting the 6 pt socket to sit tight on the bolt head. I am going to try to remove it somehow but am not even sure of how I could get anything in there to grind it down. The socket will sit on the bolt but as soon as I try to break it free it slips.