Easiest/Cheapest way to a 4bbl 318?

I'm glad to see that it will help you out.

Your miss fire on the engine could be a spark plug, like you said, but it also could be a bad wire or distributor cap.

I just helped a friend of mine fix his 318.
It was running ruff and it turned out to be the cap.
When you increase the engines timing, and make the engine have more power, it will sound even worse then before, if you have non firing cylinders.

When all the cylinders are working together, it gives the engine a smooth balance when running.
A great running engine will get smoother as the rpm's are increased

Get one heat range hotter for the spark plug and a new cap and rotor.
A v8 that burns a little oil will run much better with a hotter plug and advanced timing.