Got the diffuser in. It is two 1/4 x 18" plates welded together. I am doing my initial trail right now. Placed a 13lb bag of charcoal in the basket along with some left over hickey chips, lit a chimney and started. Placed the chimney in the basket at 0830. It took 45 minutes to hit 242F with the vents 1/2 open. Then closed them to less than a 1/4. Need to close them down sooner. At that setting it hit 282F at the 2:45 mark.
Here are pictures of the charcaol basket and the inside with racks. I did not put water in the pan. Might next time, haven't made up my mind yet.