At 1890 hours once I had the heads off I would have the valves done and the machine shop will check to make sure the heads haven't warped. I would get or you can probably down load a manual on the engine. Have you removed heads before? Familiar with internal engine work? Make sure there is no damage to the pistons ect. There will be a sequence for torquing the head bolts. Unless I am missing something generally most spark plugs have some black carbon on them from the ignition process. Don't recall ever seeing a perfectly clean spark plug upon removal.