Could be valve cover leaking too

 

The white deposits on 5 and 6 are from coolant. The fact that they are #5 and #6 also helps to diagnois this condition as the coolant outlet is directly above #5 sparkplug hole and #6 gets any leaked coolant as well because the angle of the engine slopes rearward allowing leaked coolant to migrate into its plug hole as well. The heating and cooling cycles of the engine and sparkplugs along with the viscosity of the coolant can allow coolant too eventually migrate into the threads of the sparkplugs. I would say other than normal wear on the plugs they look pretty normal from the cyl head deck down into the combustion chamber. In my opinion the just change the plugs and fix any coolant leak that may be in the area of the engine coolant outlet hose @ intake goose neck/thermostat housing and you should be good to go. Used to see this condition sometimes during thermal cycle dyno testing, cycling engines from -25 degs to 270 degs oil sump temp. We had trouble keeping coolant hoses from leaking with these extremes and the constant back to back cycles. Sometimes allowing coolant to get into sparkplug holes and do the same thing you see in his pictures.