Caping the entire head is a bit of an art but you don't need to do that for a mount. Just hang the deer by the hind legs and peel the skin down. Don't cut the hide anywhere in front of the front legs, just pull them over the legs, cut off the legs and continue pulling it on down until the hide is just behind the head. Cut off the head where the skull meets the neck and freeze the hide and head. Take it to the taxidermist and let him do the rest. I'd only cape the head as a last resort, otherwise let the taxidermist do the work. He'll do a lot better job than you ever could.