Eric.....Thanks, I cut the opening with a drill, small files and a bare hacksaw blade, cutting on the pull stroke. It still needs some work but since I may have to alter it, I left it as is.
The side vent addition wasn't so much to increase the venting as it was to redirect the flow of hot air. With the vent on the top, most of the air is drawn around the pizza and out the top vent resulting in the top of the pizza being undercooked. This was especially true if there was a breeze. In a windless environment like a garage, it's not as critical.
Adding the side vent will draw hot air around and over the top of the pizza, hopefully resulting in faster bake times and a more evenly baked pizza. That's what I'm shooting for but I'm sure I'll have to do some more experimenting before I get it dialed in.
It's been my experience that limiting the venting actually decreases the temperature. The burner needs a lot of air to support the cumbustion process and gets starved for air when the venting is less than optimum.
I'm going to Las Vegas on business next month so I'm going to see if I can score on a few kilos........of Caputo!