Maybe;
the ring gaps are closing up, and the engine is getting tight enough to stall. Oh wait, it cranks right after stalling.
Or maybe;
the valve lash is closing up, and the effective Compression ratio is dropping to less than what is required to stay running.
Or maybe;
a rod bearing has spun, and finally locked up.
Yes, I'm kidding.
But what gets me is, OP doesn't mention bad engine behavior prior to stalling. We all know that running out of gas at speed, breeds bad engine behavior. It stutters, missfires, slows down, gets mushy, and finally, even pops thru the carb if you try to accelerate back to speed. I didn't read that anywhere.
OPs car seems to just coast to a stop without drama.
I had a Magnetic pic-up do that. Actually, a couple of them.
The output on those is really really tiny, and it takes an amplifier just to bring it up to a level that the coil can work with. And the reluctor gap has to be small enough to produce a well-defined trigger that the amp can sense is a real signal. By experimentation I have found the amp to work with the gap set anywhere in the range of Zero to .030; but IIRC the spec is .008 to .011.
