Almost all of the large chicken cooks I have done were for church, and we used halves. The halves were from smallish chickens. Our process was to layer the chickens in coarse rock salt for 6 hours, then soak in a marinade for 2 hours. Then onto the grill.
For smaller cooks, which were still a couple of hundred pounds, we used large coolers, with iced brine in them. I still prefer smaller halves or leg quarters if I can. The Costco Tyson breasts work out okay as well. Just drop the chicken into the brine and let sit for a few hours then rub with a lightly salted herb heavy mix.
I'm feeling bearish, and I'm packing a Wusthof Grand Brisket slicer from MABA
"I'm Armenian...perhaps...but then again...maybe not..."