Your Lincoln Town Car's EGR valve is a great start, in fact it might be all it needs to pass the smog check. NO is created when engine combustion temperature rise above 2500f. The EGR valve introduces inert gas to the intake manifold and dilutes the air/fuel mixture so the engine runs cooler. If the new EGR valve doesn't fix the problem you want to make sure the valve is getting manifold vacuum and opening properly.
Next check fuel mixture. Any condition which would cause a lean fuel mixture will cause high NO as well. Things to look into would be defective/damaged oxygen sensor/s, clogged fuel injector/s, high compression, defective MAP sensor.
A good indicator of a lean fuel mixture is low CO.
