Right off the top of my head I think it would require you to disconnect and remove the intake pipe from the throttle body. Then remove the two bolts holding the coil cover onto the valve cover. Once the coil cover is removed you can then take all the COP's off and remove the spark plugs. From there the removal of the remaining valve cover bolts should be all that's left I would think? Don't forget to replace the o-rings and gasket when you put it back on.
As for the rusty plug I had that happen to me too last time I swapped mine. Somehow water had got down inside the #4 spark plug well which caused the plug to rust. Probably from me washing my engine and then not running it afterwards long enough to evaporate the water which worked it's way into the rear spark plug well...
As for headers... whether you go with LT's or mids you'll need a mid-pipe too. There are some drawbacks to long tubes, especially if the car is lowered or if you plan on lowering it in the future. Do a few searches in here and the 4.6 forums and see what the other guys are recommending. I went with JBA shortys myself because it was part of the stipulation with my service department for keeping my warranty intact.
U.M>
