All the 6V and 12V General Motors charging systems I'm aware of are "A" circuits. The difference is where the windings of the Field coils get their ground. In an "A" circuit, a slight voltage (about 1/2 volt) generated by the residual magnetism of the armature is picked off by a field coil winding, and sent to the voltage regulator. There, it finds a ground by passing through two sets of points, the "current regulator" and the "voltage regulator". This field current causes the armature to develop more voltage by setting up a magnetic field in the generator housing. This voltage rise continues until either the current or voltage regulator points open and prevent the generator from damaging itself, or the battery. This point opening/closing cycle happens several times a second as either maximum current flow or voltage is produced.
A "B" circuit system has one end of the field winding grounded inside the generator housing, and the regulator provides voltage from the armature via the regulator wiring (not a ground) to make the field circuit operate. Once max output is reached in either current or voltage, the control points work the same way- - - -they're just interrupting the current flow to the field coils instead of opening and closing the ground path. Virtually all Ford generator/regulator systems and a lot of MOPAR systems use the "B" circuit.
To test an A circuit generator to see if it's been polarized properly, with the engine running at a fast idle, disconnect the "F" wire from the regulator and touch it to a good ground such as the regulator base. The generator should go into max output, controlled only by the speed of the pulley. To test a B circuit, disconnect the F wire and touch it to the BAT terminal. Do this only momentarily, and don't run the engine much above a fast idle while testing.