318 hunts and surges at idle or when cruising at low rpm

I think a look at a few plugs including #8 would give a lot of info.
That's where I'd start, and then I would probably pull the valve cover and see how much those #8 valves move because this sounds like a valve issue to me also.

From doing this you might see something really obvious like a broken spring or a rocker only moving 1/4 inch.