That's a good illustration, and I have seen some folks make them that way. But, I think you will find here, the Bubba style drum doesn't have a door cut out, it doesn't use a diffuser plate and the intake holes aren't in one spot; they are spread out around the drum. They also don't use an adjustment damper on the lid; just the plain old 2" opening already in the lid.
The only reason I mention this is that the benefit of the drum is the thick walls insolate the heat; while different technology, it is a similar concept the to the big green egg. The problem is, when you go cutting doors to make it easier to load fuel, you cut into the efficiency of the drum.
I will say that the concept of the diffuser plate is a good idea. Again, the green eggs use this concept and it works for them.
I'm sure bubba will chime in here before too long and give you more info.