It's based on either the chassis sequence number, which is in the VIN that you can read at the base of the driver's side windshield or the engine sequence number. The parts reference should state which sequence range is required.

Offhand, I'm not sure where the engine sequence number is located, but it should be somewhere on the block - probably on the RH side where is can be reasonably viewed. Engine numbers are usually gang stamped on a pad that is cast into the block for that specific purpose.

Duke