How to remove this #$%$#* bolt

Hi....Help please...This is a 360 that I picked up on Craigslist. It supposedly was rebuilt, driven about 10,000 miles then parked for 10-12 years. I started disasembling the top end to take a look inside and of course, immediately ran into a problem. The center head bolt between the 4th and 5th valve is so close to the valve springs, I can't get a socket or a wrench in there to loosen it. I have also included pictures of the casting #'s, so if any of you can shed some light on what the heads are, I would appreciate it. This is my first attempt on completely rebuilding an engine so this may turn into a long lasting thread,,,,,thanks guys