The filament current of the AC701(k) is 100 mA. The 'Stabilyt replacement circuit' adds negligible current load to the supply. Thus there will be less than a 5V drop across the 47 Ω current limiting resistor at its input. A healthy NSM should provide at least 12 to 16 V at this point, and with the 39 Ω load still read above 7 V. By comparison, the original Stabilyt cells loaded the supply with around 100 mA of additional current.
If your supply (measured at the filament rectifier) collapses under the 39 Ω load, the selenium rectifier is suspect and probably has excessive internal resistance, requiring replacement. Typical replacement will be with a silicon diode bridge rectifier. Since they inherently have a much lower internal resistance, the 47 Ω resistor has been added to protect the transformer against in-rush-current surge and short circuits.
BTW. clicking on the schematic thumbnail the image opens up nicely with perfect clarity...