Hello! I just wanted to ask another opinion. I have 120 gallon cook chamber approximately 24 x 65. I cut the firebox to cook chamber opening 5 3/4" up from the bottom. I want to know if this is correct. The firebox will be 24" wide x 20" tall and 20" long. Will this be big enough? I can make CC opening bigger if need be. Also, I would like to add tuning plates. Would 4" from the bottom of CC then 4" to food rack work? Thanks!!