The rest of the story...
Confession time, the law of unintended consequences at work, again.
The reason I was looking for another crank sensor was because I had a channel fail on one of my Plasma III ignition modules (cylinders 1 & 2 bottom, not that it matters). With Klaus Savier's help I traced the problem to the hall trigger for that coil. It was dead for some reason. A resistance check with my DVM between the 3 leads of the hall switch, measured at the processor input connector, and battery ground showed open as expected for the power and ground, but about 1 kohm on the signal lead. That struck me as odd since the design and attachment of the sensor assembly should have precluded any kind of short to ground.
After pulling the prop and then the sensor assembly, I quickly realized what the problem was.
9 years ago when I was installing the engine and wiring things up, I decided that the LSE signal leads going from the sensor assembly to the processors looked too fragile. We had some urethane tubing at work, sliced longitudinally, that we used for "protecting delicate conductors in the harsh environment of the earthquake research lab where I worked at the time, so I had grabbed enough to protect the leads from the sensor board through the plenum area. At the sensor board I utilized some aluminum AN742 clamps to better secure the now-stiffer signal leads, under a couple of the hold-down screws that secured the sensor PCB to its steel bracket.
I didn't realize it at the time, because I didn't look carefully enough, but one of the AN742 clamps overlaid a trace on the signal PCB. 420 flight hours later, that clamp had fretted on the PCB just enough to wear through the conformal coating and start making contact. Turns out it was the signal trace for the Hall switch in question. A careful inspection under a magnifier revealed no damage to the trace (whew!) so I dabbed on some fresh conformal coat, got rid of the AN742 clamps and did some testing. All well, and after inspecting everything that I could see more easily with the prop off, and eventual reassembly the engine started right up, timing was confirmed to be within spec still, and I was back in the air with no cost to me other than my time and a bit of embarrassment.
Many lessons could be drawn from my experience, the first one that comes to my mind is that when repurposing things to do a job other than what the manufacturer's design intent was, have a good look around before proceeding!
