Assuming that it ran fine and now it doesn't, I'd skip the ignition test for the moment and look in the fuel delivery system for accumulated sludge. Try blowing out the idle circuit jets. Pull one carb top and see what's in the bowl. Then I'd do a quick review of ignition side: points, dist cap, maybe plugs, timing. could just be the accumulated impact of overdue tune-up, or, something blocking idle side of carbs.