Original ECO Model 98 (pedestal) used a special slotted screw that attached the pedestal to the head. When screwed in the screw could not be seen as the head went into the flange. Reference this page of my website: http://petrolianacollectibles.com/pedestal%20parts.htm
Now scroll down to #8, part number 7160. See the head is round but and it would screw up into the flange. I have restored over 350 of these meters and personally I have only had a few of the old pedestals that had this feature, my assumption is that they discontinued this early in their production, but they didn't bother to change the Parts Manual that identified these screws.