The 08 BCM will work in stand alone mode. Just need to look at the pinout list and see what all it normally controls. It uses two CAN networks, a high speed that communicates with the ECM/TCM, and low speed that communicates with everything else like radio, hvac, and door modules.

In your case pulling the steering column and other modules from same truck would probably do everything you need. No need for a HSLAN network. But you would need to rewire the key to start without the HSLAN. Currently the BCM sends a signal to ECM over HSLAN to crank engine when you turn the key. So it would not be able to do that unless you had something converting the language. Easy way, is just go straight to the PCM relay from the key crank wire and problem solved. Just use low speed network and will have 90% of what is normally used in the truck.

Hope that helps.

-K