... "rule out the impossible. What is left, however improbable, is the answer."
Or Inspector Cluseau:
"Zeh kehhs iz zolv-ed."
First, the solution (as far as I can tell): bad connection from at the coil and coil wire.
I managed to get a good test of the unilite ignition module - with all three wires attached (from dist to HyFire box, as opposed to my previous notion of taking the green wire straight to ground), a (parallel?) voltage test between the green wire (at the dist-to-box plug) and ground showed 11.09 volts when the optical sensor was open, dropping to .750 volts when blocked - roughly what Mallory indicated would be the case for their module test using negative from the coil to ground. What it also showed was no malfuntion in the unilite module, so I started looking at everything else. First stop, coil wire - when I pulled it off the coil, it just came off without any resistance, which felt wrong. So I took the coil plug that came with the Taylor wires I had (that was too short to reach from where the promaster coil is mounted to the dist), and popped it on, and got a "click" sensation. Examining the two caps, I saw that the cap for the coil wire I was using was about 1/4" deeper than the Taylor wire cap. If I pushed and compressed the cap, I could get the positive "click", but it hadn't been there when I pulled it off.
So I cut the extra 1/4" off the cap, and went out for a few spins (first with my son, then with a new neighbor who heard it start up, then with the whole family - youngest son and wife in passenger seat, oldest boy in the middle - for a golf-cart-speed jaunt around our block) with no failures. Made for a nice holiday evening drive!
What I am hypothesizing is that the cap was making enough of a connection with the coil *most* of the time, but a combination of heat (making the cap even bigger and the connection more tenuous) and vibration rattled it loose the two times it shut down on me during my last drive. Would a disconnected coil wire just shut the motor down? Seems like it would.
I still installed the signal filter/surge protector piece, and now have a spare module for the time my first one does kick the bucket!
Once again, thanks for all the help!
JLW