Real quick to interject, back in the day when computers were not all over cars and people had to think to tune an engine correctly back in the day action. Now, computers make it easier and allow a more finite adjustment but since they are so easy to use, it is easy to screw it up.
Besides the smell of exhaust gases, the spark plug was number one teller of what is happening inside of the engine since it is at the point of combustion.
You put up excellent pictures of four plugs and cylinder number 3 plug is fat as a pig rich and would explain the black smoke and misfire.
I hope you get to see what is happening and please report back. I am interested if no one else is.