If you pull the body harness that goes to the dash, the speedo should function with the grand prix cluster. The speed sensor is on the transmission.
The BCM itself and ABS are not functions of the PCM, so neither prevent the engine/transmission from working. You can't tune the ABS out because it's not a function of that controller and is not required.
You can't easily switch between dual zone and non dual zone controls, nor can you easily switch from the HVAC buttons itself if you are using the stock grand prix harness.
