[JhwShark]

So we need to check items that impact potential rich running conditions once the car has reached warm up. Since it only happens once at running temp we would assume it is not distributor related; however if (I just do not have a wiring diagram, post one if you have one) there is a Ballast resistor it is a low possible.

The smog test will reveal data at running temp. The smog readout will usually have data sorted by HC (unburned fuel and oil), CO (Air/Fuel ratio), NO (excessive output of Nitric compounds). It will/should have Maximum allowed(for the geography and any regulatory req's) Min output, and Measured. The measured compared to Max is the data to use in diagnosis. It is usually at low and moderate rpm's.

High NO usually means a bad Catalytic converter but could be caused by a bad O2 sensor. High HC means not a complete burn some causes can be bad O2 sensor that causes Components to inject wrong A/F mixture, vacuum leaks, or worn valves, even worn rings (lower prob in this case). High CO can be from similar O2 issue or vacuum leaks.

I'm not sure how the engine will run if you unplug the O2 sensor at its plug (Wired. not removing at the bung); but it is/maybe a way to see if it is bad

Spending the low $ on a smog test can help us determine what vector to take.
Jon