Good to hear your car is running well -- bummer about the NOX.

How far out is it? I understand you can reduce your NOX 10 to 15% or so by using an additive containing MMT. This is available from Walmart. 1/4 tank gas and a container of this stuff, drive it around to mix it and get the car warmed up and get it inspected.

I can't recall if your car has the same ignition setup as my 85 (I came to see your car once) but on mine, there is a vacuum hose to the ignition computer on the passenger side near the headlight. When I disconnected and plugged this hose, the ignition timing retarded about six degrees or so and stabilized. This was very obvious with a timing light. Even with the vacuum advance disabled, the car ran decent -- I expected it to really dog it down, but it didn't.

I understand you have a new cat and a newer O2 sensor. Have you checked, or
had checked, the mixture to make sure it's correct? I've not had to do that.

Harold