it would be unusual that someone put a 350 hood on a 400 car (only way it would be there..., could have been damaged, could be somebody did not want to "advertise" whats under the hood?)
if its a 400 car , it CAME w 400 hood....only later would it be swapped...of course , dealers did lots of things ,possibly COULD a buyer have ordered it that way? I`ve heard people say they like the 350 hood better...