Next time it starts to shake rattle and roll, conect your timing light and check if the flash is steady. If so put it on wire number two, three,... just to determine if you're getting a steady spark at all cylinders. If you get one that has an intermittent pulse check the plug and wire on that cylinder.
Check your points. As they wear out the gap gets larger and affects the timing and dwell. If the points look burned it may be a bum condenser, there's a lot of that going around this time of year.
As crazycars says one or two degrees of timing and a hundred degrees of rpm wont give it "missing blade" symptoms, but a missfire will. A cross fire, one plug charge crossing over into another wire, will also cause grief, do you have old wires or a couple running parallel touching?
