I'd agree that generally speaking they are interchangeable.

However, there is one concern I have:  At idle, the 2.1
runs closed loop (i.e. it considers the oxygen sensor's
input).  Without a heated sensor, the sensor will not
necessarily stay hot enough at idle.  So the 2.1 might
get confused at idle if you used a 1 wire sensor.

Let us know what happens if you try it!  Enquiring minds
want to know...

tabe johnson/87 westy