You know, I am particularly squeamish about feeding necks because I have heard a few stories about dogs chocking on them on the raw feeding list I belong to. I usually don't feed anything smaller than a wing or drumstick. I like feeding big because it gives them more mental stimulation and is better for their teeth. If you are feeding a pound of food a day, you are going to need more than just necks. I suggested leg quarters to you, because in my experience they weigh about a pound. So, I mean, toss some necks in if you want but feed some larger, meatier parts too.
By the way, Colt must be even thinner than he looks. Kai is 15 inches and weighs 21 pounds, which is his ideal weight. I hope that you find a way to pack on some pounds!