Crowbar Circuit Resistor
You can replace the resistor with a zener diode (or stack of zener diodes) to block most of the voltage and a much lower value resistor that is capable of high pulse load. 

For example, 3x 1N5956B 200V zener which will nominally add up to 600V, with perhaps 500 ohms in series. 

This will also give you a much better controlled trip point. The trigger current of the SCR will vary from unit-to-unit and is very temperature dependent.