you don't polarize the reg.. but rather the genny.
I'd opt to motor test it... slip belt off.. jump bat to armature and field.
it should spin.. if it does.. it -should- charge.. though I have seen rare cases of field problems with gens that will motor but not charge.
now.. if it passes the otor twst you are good to go.. as you just polarized it too. .. 2 birds with one stone..