As my mom said, there are more ways than one to skin a cat...
My first roaster (100 gal oil barrel) uses a pipe burner. I can't locate the parts anymore so I would use 3 cast iron burners on the bottom with separate valves instead- less work, replacement easier, at about the same cost. Be sure to use a 100# propane tank if you are using it in cool temps so that you can get the right evaporation off the tank. In the case of using a pipe, if the fire is only on the far end of the pipe- you have too many holes. Be sure to allow air in the chamber for the flame. And manufacture 4- 6" covers for your pipes so that the grease does not drip on the pipes.
My second roaster (about 300 gal oil barrel) uses an old furnace from a house that I inserted below the cooker. Only the exhaust enters the cooking chamber- no flare ups because the chamber is oxygen starved. One down side of this is the reluctance of local appliance dealers to pass the old furnaces along... It seems that they have this fear of explosions- which after going through all that work, no good roaster fanatic is going to let happen(!) so make sure that the lid is open when you light it, and religiously follow the instructions of your small grill for lighting.
nthielke@hometownsolutions.net