Do a cranking compression test on all 8 cylinders and report back. Its really not that big of a deal ,lol and you can see how the plug look. If one or more valves are off the seats, the compression test should show it as being low on compression, then you know which cylinders to back the rocker screws off
On my iron rockers the screws are all about the same height. Look to see if any screws heads seem too far in / low. Hopefully its just an open valve and its not burnt just yet