But this raises an issue related to your second question. It is not
normally necessary to avoid prevent inrush current surges with
*indirectly* heated tubes such as the 8877...

I don't know if I would agree with that. The 8877 has a 5v 10A heater.
While that is 'only' 50 watts of power, it is a resistance of only 1/2
ohm WHEN HOT. When cold, the heater might have a resistance of only .05
ohms, and represent an inrush of almost 100 AMPS. While an indirectly
heated cathode's heater element is somewhat protected against thermal
shock by the surrounding cathode, at this current level some inrush
delay might still be a good idea with such an expensive tube. It also
might prevent premature burnout of the filament transformer!