Advice on a voltage measuring circuit
Since the resistance of the load is unknown, exact calculations cannot be made.  However, as a matter of safety, it is reasonable to assume that all of the voltage (60 kV) will be dropped across R2 since it is much larger than R1 and R4. Using Ohm's law, it is easy to calculate that R2 will dissipate 300 watts. Clearly then, your proposed resistor is severely underrated. R1, on the other hand, has about 890 volts across it and will dissipate only 4.4 watts. R4 is probably OK as it has a smaller value than R1 and 6 times the power rating.  We would need to know the load resistance to be sure.