worn exhaust guides are very common on these things, if the exhaust valve is wobbling it wont seat well and you will get gasses escaping past the guide ,as far as teh valve being burnt, maybe maybe not, most likely it just needs to be dressed if the stem hasnt been worn too unevenly to ride in a new guide.
Here is where a good diesel machine shop comes in. Also if having your heads done, do not let them pull any of the freeze plugs out unless they have proper stainless plugs to replace them with as most shops will not have these and they cost a minor fortune to pickup a full set from IH ( this isnt so critical on the 6.9 as it is on the 7.3 as the 6.9 usually doesnt have freeze plugs facing teh intake manifold, that is a nasty spot for trapping moisture and rusting)
Its not too hard to do the heads in the truck, remove teh hood and radiator for room to work, and you will need a cherry picker to remove and install the heads. You might be able to get them out without one, but you'll trash the new gasket trying to set the fresh head by hand unless you are a 400lb gorilla that can juggle 13 speed gearboxes, otherwise, get the cherry picker.
When you go to put it back together, go a set of Victor Reinz head gaskets and shoot them down with about 3 light coats of spray Hylomar for a leak free installation, and hit the intake runners of the valley pan gasket with that stuff as well
You will need new head bolts and a new set of grade 8 bolts and locktite for the exhaust manifolds as well, check the torque specs carefully, there are 2 specs listed, use the lesser of the two