Your are probably spot on that the meter was a simple totalizer. There is a rectangular cutout in the skin, just under the small crank handle (raises the geared rack and lifts the sliding tube). There are no screw holes to mount a totalizer, but it could have been mounted to something inside the pump. Part #174 (2 of them) are listed as "Meter Trip Rods". I have never seen a totalizer on a 519, but I have only seen 5 or 6.