Thank for your answers Thomas... I have updated my profile as suggested.
... Yes, I do have a copy of the book. I picked it up at the university of Guelph organic conference last February.
I can include plans to incorporate a "top of barrel" gap to 2" , and increase the barrel to barrel gap to 3".
I was thinking an 8" pipe through the mass would be best....
I ran a test burn last night with just the burn chamber and everything worked good ...
I am setting this up as a portable unit also ... A base has already been welded up with a raised carriage to hold the burn tunnel and heat riser above the base . I will be putting insulation under the burn tunnel.