An old tv service book that I have shows the back of the set... it has adjustments for "magnifier height" and "mag. vertical lin" as well as the normal height and vertical lin. I don't however, see a button to switch modes like my Zenith has.
Cool set, I have never seen one.
Update: There does appear to be some sort of shutter mechanism above and below the screen, as shown in the attached picture.
This perhaps is activated by the lever arm on the bottom control?
jr