It is my understanding that meat birds are commonly kept at higher densities than that. Those numbers represent density recommendations for adult birds that will be living for a long period of time in that space. Given that meat birds are processed at 9 or so weeks just as they hit optimal size, I'm guessing that they don't have the same space requirements. I would think that 2 square feet per bird in the coop would be plenty adequate provided that there was adequate ventilation and manure management. You could probably go a bit more dense and just thin the flock a week or so before ideal processing age. You'd get smaller carcasses from those birds, but it would give the remaining birds more room during their last week's growth. I have seen some meat birds right before processing age. They did very little but sit at the feeder and eat. They had little use for 10 square feet of run space.
I admit I know little about raising meat birds. But these are the types of things I would ask over in the Meat Birds forum.
