Broken exhaust manifold bolt CM870

[Chamberpains]

Got it apart. No luck on the broken bolt bolt being any where close to reachable. Its broke off 3/8" in. I don't even know how a bolt breaks that far in. Threads look clean, so I'm hoping a good left handed drill bit will run it right out.    

Looking at the valves I see a few of them are damp. Here's a couple picks of the worst ones. Anything to worry about or button it up and run it? This is a Cummins cert. Reman engine with about 200,000 on it.