I'd like to see some pictures too. In the meantime, I can offer some suggestions. Since the point of reverse flow cookers is uniform grate temperatures, in designing one, you need to think about:
1. How best to transfer heat from the hottest air (i.e. just downstream of the firebox) to the coolest (i.e. just before the exhaust stack).
2. How to avoid any unnecessary flow restriction. Since you are essentially doubling the airflow path length compared to a standard offset, this is pretty important.
Both of these constraints would lead me to think that using a divider plate like the Lang design would be better than using pipe. Here are my reasons:
1. The divider plate provides more area for heat transfer between the "forward" and "reverse" flows, promoting more uniform grate temps.
2. The flow restriction is minimized compared to a pipe due to greater hydraulic diameter. The more uniform cross section also prevents local bottlenecks for air flow.
3. Using plate allows the airflow to turn from forward to reverse direction with less pressure loss compared to a pipe.
4. Finally, if you use 1/4" plate, you will have the added advantage of more thermal mass (i.e. specific heat) in your cooker, which will help keep temperatures more uniform during transient conditions like after opening the firebox or smoke chamber doors.
Of course, all of the above is based on considerations of flow and heat transfer. The main thing speaking for pipe is lower cost compared to plate, but I would still go for plate if it were my cooker. Good luck with your project and please post pictures.
