Situation update...
Guys, thanks for all of your responses.
I reported in error above. My volt-ohmmeter must have been frozen last night, but when pulled the alt and rechecked continuity between the field terminals and the case, I indeed had low resistance (10-12 ohms).
I pulled it apart and found that the slip rings were shorted to the rotor shaft (and, of course, ground).
Stator and diodes all ck'ed out OK.
I'm going to put in another (good) rotor and should be back in business.
Thanks again for the replys.