You set the dwell individually by blocking one set of points open with a piece of cardboard and setting the opposite set. Reverse the procedure for the other set. If I remember correctly there is a different dwell setting on dual points. For what its worth when I went to a Sun tool class we set distributors up using a feeler gauge as well as the dwell. Man that was a long time ago. As I recall you made changes on the settings to lessen the arc scatter. As cams wear along with bushings there is a lot more wiggle room on adjustment. Do as you said recheck the points and pull a little initial base timing out. Two degrees at a time. Have you tried different fuels? What octane are you running? No need to over think whats going on.