I deal with this issue all the time. Your main problem is the difference in piston heights when the fuel detonates, 9.3 mm on one side then 6.2mm on the other. Normally on an A10 a points imbalance of less than 0.002" is OK because the old girl (A10) is quite forgiving, particularly the iron head versions. The cam ring is not always the culprit, often its the machining of the cam ring housing which may be eccentric or bored crooked to the face. Your points gap imbalance is only slight, maybe 0.0015 which is tolerable. The points gap imbalance, in itself, is not a problem unless its enormous, but it usually indicates the mag timing is out as well. I would make sure everything is clean (cam, cam housing - particularly the face which mates with the mag body, shims, points heel, face of mag body) and check that the cam housing is a tight fit in the mag body, i.e. not capable of slopping about side-to-side. then set the mag up in the vice with a degree disc on it. Another point to note is that the automatic ones are easier to fix than the manual ones because the cams in the manual mags need to be loose to work! Check the firing moments with the degree disc; you'll probably find the imbalance is about 3 or 4 degrees which translates to 6 or 8 degrees at the crankshaft. It is very rare for me to have to stone the cam ring but, if I do (often on Vincents) I put a Dremel sanding burr ( not a stone as these wear unevenly) in a pillar drill and remove the smallest amount of metal off the leading edge of the overadvanced side of the cam ring. Be careful! You don't need to remove much metal to go too far!