[RGK20m3]

As the magnetic field is a function of current flow, connecting the woofer field upstream of the tweeter (with the appropriate resistance in series) should not affect its performance. But it will still result in the same higher voltages on the upper chassis as if the tweeter field were shunted.
Odd that Philco has the upper chassis plate voltages from one power supply and the screens on the pentodes from the other power supply.