This information is still rather unclear; having a manual for the meter in question would be ideal. It seems to be implied that the the meter in question is in reality an ammeter with a 500uA full scale, but is labeled to read 0~60kV on its face. In that case, yes a 120Mohm resistor in series therewith would appear to be the sort of thing needed to yield direct voltage measurements consistent with the labeling. 60kV across 120M implies 30 watts of power dissipation, with (obviously) a 60kV working voltage requirement. That’s not a common set of specifications to find in a regularly-stocked product, though something in that ballpark might be constructed using 40 VR68000003004JAC00 connected in series.
That said, a 60kV source capable of delivering >30W is something to be treated with serious respect, and I would recommend against attempting to make any direct measurements on such a source without appropriate training.