[Dirty Harry]

Thanks for the responses, everyone. This is a bit of a brain teaser. The gear on the distributor looks like new-no problem there. The valve train seems completely sound. I guess I'll start by replacing the plugs, next the wires, next the coil, next the magnetic pickup, and work my way back to the MSD box. This must be some sort of intermittent problem, because my spark tester is showing ignition, whenever I try it.

I turned the engine over and captured about a pint of fuel from the disconnected line. It looks perfect, with no water seen. The fuel in the tank is not over 2 weeks old.

Hopefully, the new wires will arrive tomorrow. I'll put the valve covers back on, install the new wires on the new plugs, and see how it acts. Replacing the pickup is a bit of a pain. I hope to avoid that. Replacing the MSD isn't too hard, but more money, for sure.