I am trying to get a little more detailed information on the polarity. And linked specifically to what erodes on the plug activated.
1st question - will Left mag and right mag have the same polarity on cylinder #1?
I think so. The mags are set up identically. The L and R used during mag assembly is related to mag rotation, not installation side. The mag uses an index to match the distributor gear to the armature gear, which is keyed to the armature shaft that has two magnets, so you will always get the same polarity for each of the 4 outputs. Though I must say that I don't know the science behind why. The gear is installed on the armature shaft with just a straight slot to index it, so it can go on two different ways (index mark 180* apart). There is no instruction to align it one way or the other when installing the gear. Yet, they always seem to create the opposite wear when installed with Lyc's recommendation.
I'm assuming yes, but what polarity is it? Ground eroding or center eroding?
Have no idea. Have never tested it and no one publishes that. Pretty easy to test. Pull the cover off and put a meter with blk to the case and red to the wire connected to the points and spin. When you can get the 3/32 drill bit all the way in the L hole, it is firing #1, so back it up 180 and spin 180. That would be the polarity for the #1 output. Normal polarity should flow from center electrode to ground and negative should flow from ground to center electrode. If I remember correctly, while we manage electricity as flow from + to -, in reality it flows the other way and I believe that the heat and thereforee wear is always greater on the pos side in a elec gap application. In arc welding, the pos side always gets more heat and modern Tig gear has the ability to favor one side of the wave or the other in AC to manipulate this effect. In DC mode, Tig uses Neg on the electode to keep the heat in the workpiece and not the un-consumable electrode.
Why do I want to know? Well, not having not been religious about the rotation and with 230hrs now notice unbalanced erosion on the plugs. Maybe just looking at then would be conclusive, but want to do some homework to be sure it won't have to be done twice.