My first guess is that mounting a scope on a Ruger Number One with a carbon-wrapped barrel is going to be impractical if not impossible. The receiver is short, but any scope that you're likely to want to use with the .220 Howell is going to be long. I doubt that the carbon-fiber wrapping around the barrel is going to be hospitable to the front base of a suitable scope mount.
I'm sure that Mike Rock can turn a barrel with a long-enough chamber reinforce to give you plenty of barrel steel out front for the forward base of the scope mount, but that approach strikes me as probably counter-productive and certainly expensive.
Mike Degerness ("carbonman") at Advanced Barrel Systems can advise you about carbon-wrapped barrels better than I can. My advice would be to use either a standard-length bolt action if you're enamored with the carbon-wrapped barrel, or a naked chrome-moly or stainless barrel if you have to use a Ruger Number One action.
