Hey PhilbrtZ,
I still say no matter what you do in the engine bay, you will fail CA smog test if the cat is not converting the CO and HC to H2O. The emissions system is a mystery even to the inspectors. You need to go to the "referee" repair shop and they will actually test the car before final smogging it. Depending on the shop and the problem, it could cost you anywhere from 200-1000 dollars. A simple fix is about 200-300. A complicated fix, well.......My suggestion is to double check the timing, and the rpm. Did you change the PCV valve? EGR valve? Make sure your timing marks are right, then, use white out to paint the mark. Disconnect and plug the vacuum advance on the dizzy when checking the timing. Yes, CA has stricter emissions laws, that's why Autopartswarehouse only has one or two CA legal cats. I got mine for about 130 shipped. Also, check the harness to the O2 sensor. These wires tend to get corroded and brittle with age. Don't give up hope,bro. Pretty soon you'll be cruising in your ZX with a smile on your face like me.
Renatodato