HOW TO FIX NOX
In your current configuration your not going to be able to fix it properly only mask it. This does not mean you can not get it to pass the smog test.
I think you have 2 or 3 seperate problems. Your slightly lean lambda calc is not causing your problem. You might not have a good functioning egr so this needs to be tested. timing spec is 5 so move it to 3 and install small tires and retest it.
Other cover ups I have seen done by other people that lower nox for a smog test, but are not legal are:
1. Install a black vacuum tee between transducer and egr and tee into manifold vacuum and hide it good using factory vacuum hose.
2. Weld up timing mark on balancer and reindex it 10 deg retarded and repaint
Your cam,header,and aftermarket cat are not helping. Changing these items are not economical or benificial.
Your headers being hotter than normal is associated with retarded timing but if you advance it your NOX will go higher.