I had 3 on a pizza pan that just fits inside my WSM, the chicks I did were 3.5 lbs and they fitted quite well, they need to be adjusted so they don't touch, if they do touch then they tend to not color up properly, and can stick together.
On the pizza pan there is just enough room round it, to lift the whole pan in or out when they are cooking, which makes life a whole lot easier!
Remember to pin the neck skin closed as, it helps keep the moisture in the body of the bird, and give them a rub down with some EVOO before you rub them down with your rub, it will help the skin get crispy.
"There's no such thing as a little garlic" A. Baer
KCBS certified barbecue judge.