Beyond what Dave posted, if you have an extra bung in the exhaust then you don't need to do anything with the narrowband O2 sensors at all. Just install the WBO2 to log and remove it when done. From what I understand, you want the wideband upstream of the narrowbands because each O2 sensor slightly modifies the AFR.

If you do want one to simulate/replace the narrowband then just look for a wideband with dual programmable analog outputs so one can be programmed to simulate a narrowband. FYI, I have read that this doesn't work as well as a real narrowband, likely because the narrowband isn't a linear curve and the wideband is a linear curve. I have never bothered trying it, I just run another O2 bung.