Howdy!
Being from Hampton, I wonder if you have ever heard of the Olde Virgina Primitive Riflemen. We hold a couple of living history events a year near Smithfield and feed the whole camp on Saturday evening. We use a similar set up to the one in your picture, just six or seven times longer. We cook 375-400 lbs. of leg quarters and it can take quite awhile. My guess is the 1/2 chickens would likely take about twice as long.
We have a method of controlling the flare ups that works pretty good, but you will need a HOT fire. Whenever the flames get to be a problem, we sprinkle the chicken with ice from a cooler we keep nearby. It works pretty good as long as you just use enough ice to control the flames. I know I have some photos of the set up we use but I just can't seem to locate them just now. If I can find them I will post a couple.