Use some Purple power or equivalent engine degreeser to remove the sludge from inside your engine. I've done this before and leaves engines looking brand spanking new when doin this, just make sure you remove your oil pan and give it a good clean too.
Just to clearify engine off, valve covers off as well as oil pan, get a spray bottle and use 100% concentrated solution and spray away at the valvetrain, and watch the years of sludge wash away. After this process use brake cleaner and spray what ever the degreeser touched, wait and see it dry or blow dry it. Get a bottle of motor oil and wet every thing inside the head with oil and done. Put your old clean oil pan and valve cover and done. No more dirty looking oil.