Jeff, Last year I did a top end on my 1986 600 my exhaust valves had a large amount of carbon built up on them also. What I did was use a dremel with a wire wheel to clean up the exhaust ports and backs of the valves. Everything seemed to be in good condition so I just lapped my valves. I am not saying that is all you need to do but Probably. While you have the head off you may look at the cam chain tensioner (actually the slider but on the tensioner side). In more then one case, I have seen them wear almost completly through. You do not want a piece of rubber and whatever that size in your motor. Just my advice.