OK, so due to the damn rain and some difficulties with my welding equipment, I haven't been able to make any progress on the build. I did however make a few design changes:
1) I relocated the fire box to directly underneath the cooking chamber. This just seemed to make more sense and will be much easier to fabricate the transfer tube without all the awkward angles.
2) I changed the doors to the cooking chamber from vertical opening to lateral opening. This will eliminate the need for a counter-weight system or pneumatic type opening cylinders. Being that this thing will be around 6ft tall, not including the stacks, it will be much easier to open and close without having to reach up over my head.
3) I changed the door and intakes on the firebox from a traditional hinged door to an integrated system where the coal/wood basket and air intakes are attached to the firebox door. There will be a gasket around the door and a set of lever locks to keep it closed tightly. The intakes will consist of a pair of 3" iron pipes with notches on the protruding ends. Flow will be controlled by screwing/unscrewing a pipe cap. The pipes will be cut in half where they run under the basket, providing a even burn. I may have an additional intake at the back of the firebox in case I need to get temps even higher.
I plan to have some kind of baffle where the smoke transfer tube enters the cooking chamber, but I haven't quite worked it out yet. It may be as simple as a piece of plate steel on a pivot.
So. There it is. Hopefully I'll get some decent weather soon and I can get on with the build.