On the really old ones it is on the side of that plate. More times than not though you'll never be able to read it. Over the years, heat, weather, occasional fires from carelessness tend to obliterate it. There were only really two body styles of the more "squared off" Genesis. The first design with a very deep box and dual rows of bars and the second design with a single row and shallower. Other than the ignitor on the VERY early designs all the internals are same for the dual row units and all the same for the single row units. The burners between the two designs are not interchangeable as because of the shallower cook box they were different lengths. Also the valve spacing is different