Minor plug wire arc

Is in total darkness a very small arc at the plug end of the plug wire acceptable? I have accell wires on my 360. I have been trying to get a steady timing on this thing. When I installed a new cam and even prior to this it did not have a steady timing. I put the mancini timing chain tensioner on at time of install with new chain and sprockets. It would vary about 2-3 degrees. Then I saw in fabo the bushing on the distributor shaft trick to hold down the oil pump gear. This brought it down to about 1 degree variance. Could it just be the old oil shaft is worn even though it is being held down or could the plug wires still have a factor. And also what is the best air gap for the dist. My old shop manual says .008 and this is a stock dist. but am using a MSD 6al box.