Folks, AT LAST, I can report that this issue is fully and completely RESOLVED!
And, in total humility, the answer has been suggested repeatedly, and could have been addressed a long time ago.
As I said in my last post, I found a new rotor that decreased the rotor-to-cap gap, and while the intermittent missing seemed to have disappeared as a result, the car would still shut off suddenly and fail to run in gear when thoroughly hot.
So, I removed the distributor and thoroughly cleaned the base and clamp to make the best ground to the block possible. I also disassembled all of the wires internal to the distributor (breaker plate to ground, points to distributor terminal) and reattached the metal ends to new wire with solder. I did the same with the wire from the resistor to the coil. I replaced the wire from the distributor terminal to the coil with a new wire as well.
When I put it all back together, I ran through the usual battery of ignition system tests. As before, the voltage drop to the resistor was about .29V, and the voltage drop from the coil negative to ground was about .18V. Spec is 0.2 and 0.1, respectively. Not seeing any change, I drove to the gas station to fill up as I was nearly empty, but I did not expect any improvement. I decided to run the full test loop I have been using just for grins and when I got to the critical point, everything seemed OK. I got back to the driveway and the car was still idling in gear! I turned the idle in gear down to about 480 RPM and the car idled without a hiccup for ten minutes. Sweet, sweet victory!
So, today I drove it to work and covered about 75 trouble-free miles. Now, finally, I can think about other aspects of this project... but first, I'm just going to enjoy driving it
Thanks for all of your patience, suggestions, wisdom, and encouragement. And, for all of you who suggested it (some of you multiple times)--you're entitled to a hearty "I told you so!"
1954 Crestline Victoria 312 4-bbl, 3-speed overdrive