On the Mustang, bank 1 is the right side (cylinders 1-4). Bank 2 is the engine left side (cylinders 5-8).
The front O2 sensors are responsible for engine management. The rear O2 sensors check the operation of the cats.
The O2 sensors to disable are the REAR O2 sensors. Sometimes referred to as 1-2 and 2-2 (first number is the bank (right/left), second number is 1 for front, 2 for rear).