Is this factory? If so what year has the sensor bung on it? Just curious as I just tapped mine for a 3/8 sensor probe.

 

That is a factory housing on my '85/22RE. Various versions had fittings for sensors including the A/C high coolant test cutoff sensor (what mine is), or for A/T equipped vehicles, similar feature or for turbo (22RET) equipped vehicles where there is a similar sensor for the ECU to prevent engine overheating. So you can have 0-3 holes for senders in the t-stat housing depending on what features are on the vehicle.