Hanging ribs is not a huge problem, just make sure you don't over cook them. The real problem is not being able to see the cooker, gonna be hard to explain how to run it. 12 racks is going to be a lot to fit into a 55 gallon drum, when you say barrel, do you mean a steel drum or something larger?
I'm feeling bearish, and I'm packing a Wusthof Grand Brisket slicer from MABA
"perhaps...but then again...maybe not..."