Do I have a burnt/burned valve?

On my 70 318 there is a miss or a skip when at idle and applying the throttle. It has dual exhaust and it almost feels like the passengers side exhaust sucks in real quick in a consistant pattern while idling.
I am thinking that because of the year of the engine, and stock heads that unleaded fuel may have caused a burned/burnt valve. I pulled the plugs and cleaned them up and they all looked to be in good shape. Can bad/dirty points simulate this, or do you think the heads need replacing. I have a set of mid 80's heads laying around I could bolt on. I am chnging this motor out soon, but I want to make sure it is running good before I pull it.
Thanks for any info.
I could probably take a video and post what I am talking about with the exhaust.