Hi Jeff,
Welcome to the amazing world of charcoal gasifiers. Rule #1 is use well cooked charcoal and rule #2 is do not force air into the air inlet. By pushing compressed air into the air inlet, you create a mini blast furnace. Yes, the charcoal gas exits as fast as you push compressed air in, BUT, the velocity is much greater than an engine sucking would create. There fore excess heat. If the engine sucking created too much heat, then the air inlet, outlet and reactor must be increased. Your are using a 3/4" nozzle so your engine HP should be no more than say 10HP.
Why did you use compressed air to start up the reactor instead of using the bilge fan? The fan is very adequate for starting the unit so am just curious what you were thinking. Just helps me understand what people are thinking so I can better understand the issues as they see it.
As for making charcoal, it is very easy with just a steel drum with a lid. No need for doors, stone, brick or other fabrication. I don’t want to throw water on the work you have already put into your kiln, but it it is not necessary. I have made very good charcoal by bulding a fire in the bottom of a steel 55 gallon drum. As the wood burns down, I add several more logs. As they burn down, add some more and keep repeating. Use dry wood and add the next round of wood a little before the previous load has turned to coals. Over several hours and a dozen times of adding wood, you will have a barrel half full of hot charcoal so put the lid on and let the coals cool off. Open it up 12 hours later and remove the charcoal. Any unburned pieces go back in the next batch. This is the simplest way to make charcoal, but takes a fairly vigilent eye. Go to youtube and search on “Gilmore charcoal” to see the way I use most of the time. You can also go on the yahoo usergroup charcoalgasifier and look at the files section for more info on making charcoal and the operation of a Kalle gasifier. (check out the files section of this forum too. I forget if I had the charcoal info posted 
)
Another important aspect of the charcoal in the Kalle gasifier is to grind it to a certain size. This is catagorized as “Fine” charcoal. I must not pass a 1/8" screen but must pass a 3/4" screen. The small charcoal size is extremely important to the operation of a Kalle style gasifier. It you are using larger size charcoal, the reactor will heat up as the hot gasses find easy passage through the course char.
Keep it up and let us know how you make out.
Gary in PA