Thanks everyone - appreciate all the input! Good point re pulling and seeing what goes on.
Some 960s only have one sensor. They are a single cat with 2 inlets, one outlet.
This, exactly this. In detail:
2x 60mm pipes from the manifold down under the drivers floor to the right of the driveshaft and merging into the cat with a multi wire O2 sensor that I'd definitely keep in the FRONT of that cat right in the middle in the merger of the 2 60mm pipes. A single wire sensor is on the output of it. Then out of the cat is a single 60mm or maybe even 58mm but it might be deformed. That gets quite heavily squashed as it goes under the cross member that sits just in front of the fuel tank on the opposite side.
My next question, and I'll just reuse this thread rather than spamming another one, is what people do with 3" exhausts under these things:
There is 70mm from the compressed part of the cross member (welded in one) where it's ribbed presumably to minimise heat transfer to the bottom of the existing tube which is lower than anything else under the car. So say we left 5mm above then we'd still be 5mm even lower and more likely to scrape on things than with the stock exhaust.
Does anyone put a holesaw through that cross member and weld something in to give some air gap and allow a full 3" without contact and without going lower than stock, or maybe even a bit HIGHER than stock?
To the person that cynically said "it doesn't make enough power" this is not about power, here's what I'm doing with all of my cars:
1. Cat delete and sell - money funds mufflers and bends and tube to replace and upgrade
2. Install only 3" straight through parts ready for later power upgrades
Eg I had a rusty falling apart muffler fail inspection on my Stagea wagon and it got a 3" section with cheap stainless muffler and cone-step up BEFORE the vband coupling at the front and cone step down AFTER the vband coupling at the rear. Pretty soon I'll order the new rear muffler for that car and all I have to do is cut the vband flange off the old rear muffler and fabricate the new 3" stuff to go in there and mate up and not rattle.
Cats aren't going to be worth the money they are now forever, EVs are coming and coming fast, as soon as demand falls cats will lose their value to some extent unless something outside car manufacture produces demand. So I want to cash them all in ASAP and upgrade what I can at the same time on all the cars I have big upgrades for.
For the 960 wagon, tomorrow night I'm bringing home a slightly grubby but smooth running2004 B6294T wrapped in a fairly clean by deregistered (plates no longer live, a bit expensive to get live again) XC90 - it won't be going in for a while and expect more n00b questions on internals and limits thereof and various engine details in future, but the goal is, once the car is sorted chassis wise and interior wise, to upgrade the trans a bit with a shift kit and maybe manualise it, and drop that or something based off that in. 270hp stock, but cams/coldside/hotside will push that north of 400@crank without even raising the boost.
So yes, 3" will be justified, and I'm forward-looking in all the changes I make to all of my cars.
at some point, maybe soon, I will categorically prove this wrong. Have you ever driven with an undersized exhaust on any engine? Guessing not. I have, several times in various ways 
