1977 350 ci tune-up

[InsouciantSoul]

So popping the hood, i heard a slight "ticking" noise, coming from the drivers side, rear of engine. Putting my fingers against each spark plug i noticed the one in the back was rattling. (I just replaced the plugs wires and rotor a few weeks ago) Tightened her up, started her up, still a ticking. I decided to take it off entirely to see if it was somehow burnt out. It had a fair bit of oil around the gasket part, maybe it was cross threaded? Anyhow it broke taking it off - so I'll have to wait until I go buy a fresh plug to know if that was the source of the ticking noise. Could it be something else?

While I'm there, I'm going to buy a new fuel and oil filter for her, because I haven't since I got her a few months ago. Is there a particular kind that is best?

I want to clean the engine out good, is there a certain additive I should put in my gas for one tank? Is there something I run through the oil reservoir while I change the oil? Is there a certain/best kind of oil I should fill her up with?

This is my second truck and first one I've taken care of, so I'm a big noob to it all. I've heard something about "carbon build up" ? *shrug* educate me please!