[MrFixr55]

That may be a typo somewhere.  The 12 uF cap + lead and the input to the field coil (also serves as a choke) should be going to the cathode of the 84, Pin 4 per the RCA Receiving Tube Manual RC12 (1934).  Pins 1 and 5 are the filament (heater), which is insulated from the cathode.  Pin 5 will either be chassis ground or 6VAC above chassis ground, as this tube is heated by the same winding as the rest of the tubes are heated.  So, if the input to the filter is actually connected to Pin 5 instead of Pin 4 of the 84, then the radio will not work.

The "other guy" put 20uF caps in series, likely to lower the capacitance to somewhere near the spec.  Back in the day, electrolytics were rated - 20% / + 100%, so a 12 uF cap could be anywhere between 10 and 24 uF.  I don't think that using 20uF caps in the power supply would be too much of an issue.  It would raise the voltages a little.  The only issue here is that both RCA and Sylvania indicate the cap value for a cap input filter is 4uF.