1991 240 Volvo Car Emission Fails with High Nox?

You're correct in assuming the egr system as the culprit - either that or your engine is overheating and I suspect you know if that was it.

I tried to have my car inspected today, and the car passed all but one test. The NOx test. To pass it has to be 1163 ppm, and the car after running for an hour scored 2959 on the high side, and at the lower speed it was 3003.

I am considering the EGR Valve, but those numbers seem really high for a clogged EGR. The HC passed, so I know it's not the catalytic converter if both NOx and HC failed.

Do you think an EGR, Oxygen Sensor, MAF cleaning, PCV valve replacement buy me that much reduction in NOx?

You're correct in assuming the egr system as the culprit - either that or your engine is overheating and I suspect you know if that was it.