All four cans are now in place and working. This shows the "gas drip pan" in place on the top of the second coffee can. It has a 3 9/16th diameter hole, and is aligned with the 3 inch diameter focusing can just below it. Thanks to Paul who made me aware of this common TLUD design feature.
Note: The top coffee can is just hot enough to soften the pain on its sides, but not to burn it! At this stage, the bottom of the Weber can is cool enough to touch. The gap between the two coffee cans is about two inches and allows plenty of secondary air to enter the system. I also expect that the two outer cans help to keep the inner cans a bit cooler and more evenly heated. I do not think that even the burn pot has any cherry red sections.