Not saying it cant be done....but should it be? Sounds like you have an awesome grill...cutting into it could mess up its intended design. A smoker and a grill are 2 totally different designs and everytime someone tries to combine into one unit it is a long journey of compromises that never ends with complete happiness of either function. With just a little more work, you could build a dedicated smoker.
I would say that you are on track with your design and could work but id be concerned with the amount of space from the proposed baffle plate to the rack. Looks like it might be pretty close and not give the airflow you are intending.