Update:

Well, disconnecting the coolant temperature sensor sure doesn't work (engine way rich, barely idles).

The sensor is at 250 Ohms at ~85ºC. I wired a 150 Ohm resistor in series with it this evening. Seems to run okay this way, no obvious mixture-related issues. Don't yet know about the hot stall, though.

Thinking about it now, it would have been instructive to see how the engine behaves with a short across the sensor. Oh well, we'll see how hot the weather gets tomorrow!