What's your fuel pressure at idle? What is it when the sputtering occurs?
Are your flywheel and balancer both of the 28 ounce variety?
Are your spark plug wires touching each other anywhere after the distributor cap?
You said it ran the same with the distributor vacuum advance connected to either the full or timed port, yes? This is a problem. There should be quite a difference. What carb are you running?
Have you inspected the spark plugs to see how they look?
try unplugging and grounding one spark plug wire at a time, and see if you can find a dead cylinder. If you pull a wire, and it runs no different, you've found a dead cylinder.
Answer these questions, and we'll go from there.
