I looked up a DIY ESL amplifier design from the same era (1968). In that design the author used light bulbs “to equalize the voltage to the capacitors” in the high voltage section of the output.

After reading that, I remembered that Nelson Pass has an amp design that uses four standard base light bulbs in some sort of regulation scheme.

It may not represent an component of a crossover section as I originally thought it might, but I find it very difficult to believe that it’s intended to terminate the panel leads either.