Bush Dac 90 Capacitive Dropper

[Aerodyne]

Here's my take on this: forget the existing dropper connections. Feed the rectifier anode as Lawrence says, using something in the region of a 300 ohm resistor in series. Fit the output of your capacitive dropper plus the series surge limiter and connect to V5 heater. The use of the discharge resistor is probably a good idea but I'd see it as optional. 100k is likely to be at the low end of a value I'd use but should be OK. I'm assuming you've worked your dropper value using a mains input of 240V.
I would also rewire the on-off switch to work on the live input. Replace the mains RF bypass capacitor with an X rated high voltage component or remove it entirely, refitting only if essential.
Tony