I have one of the last 2001 3.0i's, built in July 2001. It has the high tech cluster. I do have the coolant level sensor. The wires for it come out of the fat bundle of wires going to the ABS unit right near the bottom of the coolant tank. So the 2 wires from where they leave the bundle to the sensor at the tank is about 4 inches.
It seems like some E53's had the sensor, some did not. For the 3.0i's, it could be the high tech cluster that determines this. Not sure. This was discussed in the following recent thread:
https://xoutpost.com/bmw-sav-forums/...l-coolant.html
I agree it would make sense if all the replacement tanks have the sensor - cheaper to put it in all of them than to manage two different part numbers.