You piqued my interest with this project. You call the project a BBQ pit and an accessory smoker. I've been cooking with every emaginable combo of barrels,pipe,sheet metal and masonary for years and would like to build something now. What range of tempatures will you run in the cook chamber? What tempature range for the smoking box?
Probably as low as 150 and at the most 400 or so in the cook chamber.
Smoker be lucky to ever see 300 and most likely run 100 - 200.
The cook chamber will probably have to run 100 above what the smoker needs to be when using. Just a guess.