[ewill3rd]

I have to confess I haven't paid much attention to the exhaust on Catera, rarely do we have true dual systems on any of our cars.
There is typically a shared resonator or an H pipe. If it has true dual exhaust it changes the way the test is done actually, they would probe both pipes and the computer will measure them together. If it is true dual then it would be easy to tell which side there is a problem on.

I am really confused as to why you are doing all this stuff without even testing the car. You don't get arrested for failing the smog test, you just have to fix it.
I mean it is great that you are doing all these things to help keep your car running right but spending all this time and money because something "might" be broken seems awfully strange.

The AIR pump cannot be any sort of problem.
It only runs in open loop on a cold start and cannot cause a failed emissions test unless it is missing or a current code is set for it which would turn the MIL on.
AIR is in place to lower cold start HC emissions and pretty much for no other reason.
History codes are no problem, but if a code has the MIL turns on during the test it will fail if the code is current.

As far as I can tell we are trying to diagnose and fix a car that isn't broken yet which makes it really hard.