How about doing a raised grid, that way you would't have to do any drilling or welding on the drum. Get some carriage bolts, fender washers and make feet on the top grill and get an 18.5" or bigger grate and just set it on top of the main grate. You could make it 3 or 4 inches high and use the Weber lid.
Brian - Left Hand Smoke BBQ PNWBA 2010 Team of the Year
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