Sounds like doing a basic tune-up, an Italian Tune-up, check for vac leaks and try a re-test. cleaning the throttle body is optional but a good idea. Flame trap and hoses is the same.

Checking the O2 sensor to see if it is in spec would be wise.

So I will guess your cars is a 1992 240?

"adding CRC 05063 type stuff"

Not sure what this is?

When was the last time you did cap, rotor, plugs, wires, oil change, air filter? Are there any stored codes? How does the car actually run and what type of gas mileage do you get (stick or auto, type of driving?). Last time you cleaned the flame trap and associated hoses? Last time you cleaned the throttle body? Have you checked for vacuum leaks?

My best guess, we could get you to pass everything but the NOX with just a good tune-up, including an "Italian tune-up" if you normally drive the car like a grandma, and getting the car good and warm. I am not as confident on the NOX.

If this is the same rolling-road test I see for most pre-ODBII cars, even a decent running 240 with a working cat should pass. Do a search for all the other threads on failing emission for a 240 and check their fixes and the results. wWith the except of the California and Ontario Canada folks, it seems that most of us can get a car to pass without resort to a new cat but think DC (also making an assumption here based on your user name) mirrors the California testing method.