James, cannot comment as i havent tested but I'm glad to see im not the only long islander doing a WSM turkey this year. Im doing an 18 lb'er in my 22" WSM in East Meadow.
The one comment i can add is that dark meat needs more heat then the breast, and the edges of the WSM which aren't protected by the water pan, so if its a tight fit i would try to put the leg side of the bird closer to the warmer edge and the breast closer to the cooler center.