Check engine light codes P0420B and P0430 on 1996 Ford Taurus

These obd2 codes indicate a failure for both catalytic converters (CAT) of this engine but the problem is the CAT is pricey (almost $1000 for both). How do you check the efficiency of the CAT?

Symptoms:

Both obd2 codes show up within 5 minutes of running the car.
Pinging when taking off

Here are a few common causes of CAT failures:

Poor quality gasoline fuel
Engine misfiring
Faulty oxygen sensors or not connected properly
Damaged exhaust system
Faulty coolant sensor
Faulty mass sensor
Excessive oil consumption

From the list above, if the problem is a sensor failure like oxygen, mass or coolant sensor, it should show when the codes are scanned. The same goes thru if there is misfiring on the engine. Take note that when the mass sensor is dirty or has failed, sometimes it will not show as a code. Try servicing this first before doing anything or replacing the CATs. Then monitor the readings of the oxygen sensors behind the CAT by manually making the mixture either rich or lean. This type of engine has 2 upstream oxygen sensors and 2 downstream oxygen sensors located after the CAT. When working normally, the downstream oxygen sensors fluctuate less than the front upstream sensors. A failed reading on the downstream oxygen sensor usually indicates a breakdown in the CAT. If the sensors checked out OK, replace the CATs but make sure to use Ford OEM parts.

Notes:

This assumes that the engine timing is set right after disconnecting the spout connector.
If you can get hold of a laser thermometer, measure the input and output temperature of the CAT. There should be 50 degrees difference after the engine is at operating temperature.