I mislabeled the previous partial schematic illustrating the "shunt" resistor for the ART-13 plate current. Nothing escapes the Eagle Eyes of Robert Downs.
Shown below is the corrected schematic.  BTW the full schematic is on page  96 of Vol III of the Surplus Conversion Manual.  I've also traced out the plate meter circuit and it is attached.
BTW Robert has excellent reprint of the  ART-13 series manuals, my wife says they small good as they  do not have any musty moldy smell.
Z