Hmm Bruce...
By the (Chev CMP) book you have a two pole, shunt wound generator (You in fact, have three poles) Hence two poles are the armature. The other provides excitation via the Field.
Remember ANFEE+ (Mike Kelly will know the good old Morris theory) Armature, Neutral, Field, Earth. Floating earth...
Do not connect the third set of brushes.. They will alter the charging circuit. They are just a redundancy option if you stuff/wreck the field windings.. or they burn out.
As I do not have a Chev & I
presume this is a CMP generator, then I guess that the two poles are the correct number of windings.. This should give you the desired output.
Otherwise you will have to do a trial & connect the
third set of windings & measure Voltage output, & current output. Rotating the generator at the 6 cylinder engine RPM of about 800-1200 RPM (around average charging cct). Which is easy with a washing machine motor bolted onto a test bench. Then you can determine if you have sufficient voltage to charge your battery.. (this is done connecting the third set of field windings, which in your case should NOT be necessary!
A Growler will only determine if the windings are serviceable..not the output..
How will that output look????
It will be a very ripply DC as each rotation induces the voltage to the armature. You wont notice that with a multimeter (selected ON DC VOLTS) but with a Cathode Ray Oscilloscope it will show up as a positive ripple voltage.
Gee you blokes test my electrical theory!
Hmm don't ask me about Ward Leonard lifts.. I had to learn them for Aircraft carrier theory
Now 26 years on I am teaching generator theory!
Ian