failed emissions

Nox is lowered by the catalytic converter and exhaust gas recirculation emission system. Raised compression and other engine modifications can also contribute to high Nox emission. High HC can be caused by a slightly lean condition, or poor catalytic converter operating efficiency. Its a delicate tuning balance to get the balance right between CO, HC, CO2, NOx, and O2. Adjust your valves for starters as part of a tune up, and replace plugs.

Because of the age and mileage there is a lot of things that could be worn out. The first thing I would do is to make sure the engine is in good mechanical condition. This can be done by looking at the engine's vacuum readings. A sound engine is a great vacuum pump and the readings it gives will reflect the condition. All the little things make a difference too, compression, ignition timing, valve timing, valve adjustment. Oxygen sensor readings are important in the emissions and I would make sure the sensor is working properly with the correct readings. I would also take a good look at the catalyst to make sure it's working as designed.