Ralph, I would add to your list the experimental reversal of cartridge phase on one channel-- no matter what the ohmmeter says. Incorrect relative phase will definitely shift the image to one side.
Also, has each tonearm wire been checked with an ohmmeter to confirm that there are no leaks between the wires or from any wire to ground?
Also, has each tonearm wire been checked with an ohmmeter to confirm that there are no leaks between the wires or from any wire to ground?