Block off the curves past ~200 volts. Draw a horizontal line at ~10 mA. Interpolate a bit to generate a grid curve at ~3.7 volts. What plate voltage do the load and grid lines cross? By the curves in my sheet, it looks like ~90V. Perhaps a third LED to raise the plate voltage to ~120 might be a good idea...try both and see. You can clip lead a short of one of the LED's if you want to put in three the first time.
regards,
Douglas