Don't you think it would be fair to send a mail to Kepco asking them if they permit you to publish this schematic or not ?
Look easy to build ?
You don't even have the voltages of the secundaries of transformers...
It is a 2000V 100mA power supply with floating output.
It is quite different of Heathkit IP17 power supply because it is a much higher voltage and it is a floating output ....IP17 has negative polarity grounded.
The first tubes (you name preregulator) are limiting max Vak voltage (and also max. Pa) of the regulator tubes.
When Vak of the regulator tubes became higher than a fixed value, preregulator start blocking and limit this voltage.
Control circuit is referenced with + output polarity, for this reason there is no need of high voltage drivers transistors.
As everyone of the polarities may be grounded , the control circuit can be at high voltage compare to ground.
For sure, there are a lot of precautions of safety.....(potentiometers and switches mounted on isolating board, plastic axles, ...)