I bought a second FAST analog O/2 kit for the passenger side exhaust. (My exhaust is setup as true duals with no crossovers.)
I found that even though I marked all four metering screws in the full inward position (12 o'clock position with permanent marker), and I backed them all out the same amount, and I used the drivers side sensor as a reference. Even though I setup the passenger side the same as the drivers side (existing O/2 sensor), the idle was different from drivers side to passenger side once I had the dual O/2 sensors installed. This surprised me because even though I had both sides set the same, that the passenger side gauge was now showing about .4/.5 difference in the readings. It didn't take long to have both gauges reading the same, but the metering screws are different from the drivers side to the passenger side to achieve the same reading (within .2 on the gauge).
Another thing that I found was that when adjusting the passenger side metering screws, they mainly affected the passenger side O/2 sensor, but they still affected the drivers side O/2 sensor too. It took a few tries to get both sides balanced out, then I took the car for a drive. Overall, the two gauges were within .2 of each other with the carb setup the same from side to side, except for the metering screws. Cruise and WOT were also within the .2 or so which is close enough for me.
So after adding the second O/2 sensor, the main surprise was that setting the drivers side metering screws exactly the same from side to side did not show the same reading on the gauges. But cruising and WOT were mainly the same (passenger side was always .2-.4 leaner with the carb setup the same side to side). If I get enough energy, I might try adding slightly richer IAB's on the passenger side just to see if that brings in the passenger side O/2 reading at cruise a little closer to the drivers side.
The attached picture shows the difference at idle in P before I shut off the car for reference.