Don worry about the carbon buildup in teh exhaust housing... is it thick with buildup or just black? cause if its just like stained then just leave it alone, cause after 100 miles it will look the same anyway. If its all carboned up, then scrub it with a small wire toothbrush. WHen you are done sand it in a couple stages then wash it again and it will look just fine. You should probably replace the valve seals since its off anyway. And if the head has a lot of miles on it, i would also consider regridning the seats.