[Arran]

Quote Mr. Fix "Most Philcos of this era that have Push Pull output used the "screen grid resistor tap" method to get the inverted signal needed for the other tube in the Push Pull pair. Most of the 1941 sets used the '41 pentode, which is electrically the same as a 6K6. The B+ on these sets was only about 180V. I don't know why this was the case, because 250V is more common for tubes of this vintage."

I may have misspoke about what that chassis had for power output tubes, it was actually the Canadian version of a 40-180, so I can't actually remember whether it used #41s or whether it used 6K6Gs. It's in a box in a basement closet so I haven't looked at it in some time.
Regarding the low B+ voltages, most of this series of sets used an #84 or a 6X5 as a rectifier, which like #41s and 6K6s was popular for use in car radios of the period. I think the reason for the low B+ voltage was so they could power an 8 tube set using an #84 rectifier, at 250 volts the current output is only about 70 ma, run the tube at lower voltages and it can deliver more current without causing a heater to cathode short.
180 vdc was about what a vibrator supply could deliver in a car radio of the era, and since the set had push-pull 41s/6K6s the output was still a respectable 5-6 Watts, with lower distortion then a single ended 42/6F6. These sets were built to a price, hence why they used the "screen grid inversion" trick, less power then with a proper phase invertor tube, but it was one less tube they needed to use. It's strange that they did not incorporate a phase invertor tube into the 41-287 rather then wasting a socket on an extra double diode detector tube, it would be tempting to rewire the set to add one, then again maybe that would overtax the power supply?
Regards
Arran