No you don't need a WBO2 for an A/F gauge, you can add a regular O2 sensor or splice it to one of the O2's already on the car. I have mine spliced in to the first O2 at the top. It's not very accurate just tells you your running rich under full throtle and moves around the rest of the time, except when down shifting to slow down then its lean. Hope that helped.
Orng1/Bob