[morzh]

So, after the resistors had come, I installed the 150 Ohm resistor and the initial voltage went  down to 155VDC. Consequently the rectified voltage became almost 118VDC. The plate voltage that were supposed to be 91V became 82-85V. Much bettertthan it was with the selenium rectifier but just a tad low. I wanted a bit more and I had some headroom now, so I took twlo 249 Ohms 5W resistors in parallel, made 125 Ohm 10W one, and the voltages became 123V and 91V respectively. I am OK with it.

   
   

Then I installed the 6.8uF cap in series with the filament string (convenient place was between the GND and the pin 4 of the 19T8, the discriminator-detector).
The voltage came down from 128V to 114V, which is almost ideal.
   


The diode/resistor mod looks like this:
   
   



The chassis underside now looks like this: