To calculate the resistance required is simple ohms law, assuming the meter is 1mA FSD, and you want to read 60KV FSD, simply divide the voltage by the current, so 60,000/.001 = 60,000,000 ohms. With a 100uA meter, it would (obviously) be 600,000,000 ohms. You should subtract the internal resistance of the meter from this value - but I think it's fairly obvious that a couple of 100 ohms from those values is a waste of time!.
You also need to be concerned with the voltage and wattage ratings, with a 1mA meter it will dissipate 60W, and with a 100uA meter it will dissipate 6W. Also resistors have voltage ratings, usually only a few hundred volts, so you need to use multiple resistors in series to withstand the voltages, or a smaller number of special high-voltage resistors in series. These special resistors are usually very high values as well, designed for this type of use.