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

You still may have a problem. The pop-pop-pop is a tell tale.Disabling a plug, introduces an unburned A/F charge into the header. When it catches fire from another cylinder, AND air from somewhere, it explodes and the expanding gasses rush down the pipe and it makes a pop,usually heard out the tailpipe.. So Ima guessing the timing may be a little late and the header has an air leak into #8 pipe. Normally an air leak into a manifold is no big deal. But an air leak in a primary pipe destroys the strength of the scavenge pulse, and that means that cylinder will be down on power when the others are pulling hardest. Just something to think about.The air leak could be at the end of the header where it bolts to the exhaust pipe,in which case it would not effect power. But if the primary pipe is pulling in air up near the head, I would be scheduling it in for a gasket,no hurry.But if you are running a manifold, I would be in a bigger hurry to fix it, as this situation could damage the flange. Could damage.Not; will damage.
There is another possibility. If an exhaust valve is hanging up, when the descending piston is trying to pull in a fresh charge, then the piston may try to pull atmospheric air in through the tailpipe.This will/may also cause popping, as the fresh air meets the burning charge. This can be felt by putting your palm over the tailpipe on an idling engine. When the valve sticks, it will seem to suck your hand onto the pipe. If you have a crossover, you will have to cup both pipes, or plug one. This is more noticeable on vehicles with very short systems like lawn and garden equipment.Or small motorcycles, but I have witnessed it on cars too.