Wow.....
This page shows a bit more information on the P0056 Error Code..
dtc-holden-commodore-ve-p0056-d1599m19.htmlThere are two HEGO sensors fitted to each side (LHS pair and RHS pair) of the engine.
(One is before the Cat, and the other is after the Cat).
It looks like out of the 4 that you have, only 1 is possibly working / connected.
I would jacking up the car and checking the wiring connectors for these things, to make sure they still exist,
and are connected to their respective HEGO sensor.
This image shows the HEGO sensors fitted after the Cats.

There will be 2 others, one fitted to the LHS header/extractor, and the other to the RHS header/extractor.
If these are connected, then it may be possible that when the wires were ripped out, they may have shorted and damaged the ECM.
(Engine Computer), which probably wont be cheap (or easy) to replace...