so here's what I did - I started the car with everything in place as it was (still charging full bore) and I measured volts at the battery and got 14.30 and then at the Ignition 1 terminal at the ballast resistor - 13.85. That's a pretty significant drop. Since I had another alternator, I put that on and restarted the car and low and behold the ammeter started coming down over 5 minutes. Voltage at the battery charging is 14.3 and steady, disconnecting the battery positive cable and checking the battery itself - 13.76. I let the car runs for 20 minutes and checked it all again: 14.3 at the battery connected, 13.78 at the battery disconnected, 13.76 at Ignition 1 at the ballast, all holding steady. So just out of curiosity I got the voltage regulator that this all started with and put it back on the car - after some charging after the start it all settled down to the exact same figures as with the new voltage regulator.
Thank you to 67dart273 for the help - I think I understand the system better than I did when I got up this morning! I'm going to take the bad alternator to a local rebuild shop (1 guy who has been doing this for 20 years) and see if he can figure out what happened. I was disconnecting the voltage regulator at the regulator itself (two wire big plug) and that shut the alternator down every time, and yet replacing the alternator fixed it - like you I don't understand how this could be.
mikebee - thank you for prompting me to switch the alternator. I still don't understand how this could be it. but there is no arguing with success!!!
One thing is for sure, I think I should get off my rump, pull out my wallet and replace the 44 year old forward wiring harness. Parasitic losses in a dozen places could account for the voltage drop and the old wiring under the hood, subjected to outside air, and the heat of 44 years of running the engine is usually toast long before the stuff inside the car. The car is a show car, but gets driven to shows hundreds of miles away (that's 3/4 of the fun!) so the last thing I need is an electrical issue 500 miles from home!