You could try getting the engine to operating temp, closed loop at idle, then disconnect the O2 while the engine is running and see if the ECM goes to open loop. Of course within a short period of time the ECM should throw a CE light and a code 44, maybe a 45.

Does the 079 ECM learn parameter for a sensor like the later non-OBDII cars do. On those cars when you replace a sensor the ECM needs to relearn the parameters of the new sensor. For instance a new MAP sensor may read 4.25 vdc at idle, the old sensor may have been 3.5 v. The ECM needs to relearn the idle voltage which is now 4.25. Our cars have VAC sensors, their output would be opposite of the MAP sensor, low voltage at idle, high at WOT, just to clarify.

I had a set of the TES also installed on my L69, high flow Random Tech cat and 2 1/2" mandrel stainless cat-back. On the TES the O2 is located pretty close to the head, still in the engine compartment. On full length headers the O2 could be 30" downstream and under the car floorpans. One of these days I'll have to shoot some exhaust pipe temps with the pyrometer to see how much it changes as you move away from the exhaust port. I have used that meter to check individual temps of each cylinder as it exits into the primary tube. Engine dyno headers will usually have a thermocouple in each pipe to monitor each cylinder exhaust temp. You can use that info to determine if a cylinder is rich or lean.

Currently running Hooker 2050 emissions headers on the new engine, again smog police in Pa necessitated that. I did have to move the O2 bung from the left collector to the right collector, this due to using mechanical clutch linkage, the Z-bar would just touch the O2.
Bob