Bob, great to see interest in downdraft charcoal gasification! I realy do feel its the next step for us all.
Just one correction thugh. The buty of a charcoal gasifier is that it doesent need a restriction. A restriction is important in a wood gasifier mainly to concentrste the heat and turbolence in order to crack tar. But with charcoal, we rely on the intense heat from the burn it self to do the job for us.
Wich brings us to Bruces idea. Couple of problems. As Bob correctly obsurved, with a cross draft (wich Bruces idea kinda is) you never realy get a horisontal glow zone but it rather extends up as a updraft. Better, but still not perfect. Plus as load decreases steam and tar vapours can be sucked from upper layrs around the glow zone and trugh the gas outlet pipe wich defeats the purpose.
What we need is a plane of superhot charcoal with no possibility of any steam escaping around the “hell zone”. This way we fully utilise the ability to burn less quality charcoal cleanly and we can add and meter water to the reaction precisely by adding our dry charcoal fuel a certain amount of water wich gets released as neaded automaticly. Exactly like wood does in a wood gasifier, only cleaner, faster and safer, more controled.
The lack of restriction neaded gets rid of some of the drag, meaning we make better quality gas and more of it for the engine to feed on. Thats a recepie fore some well fed engine horses 
This is why l proposed 2 opposing flute pipe nozzles. I will make a skech later but l realy like Bobs plan to make this weldless! I am sure it can be done!