I've cooked chuck roasts directly on the grate, dead center. Using a 3x2 snake method. I forget now how long it took.
I've also cooked it in a big foil roasting pan to make Pepper stout beef.
I've always manually arranged the charcoal for a snake. Poured out will work, but you might get an uneven burn and end up with temp spikes. (which for a chuck roast won't really matter)