Check out the Pedersoli Hawkens. They are pretty true to type and are available in walnut and maple. .54 is as large as they go, I believe. They also make a fast- twist that handles conicals. They aren't cheap, but based on the Mortimer I had and a 1861 replica I saw a fellow hunting with last season, quality is good. The Lyman Great Plains rifle is fairly authentic looking and less expensive.
Most of the "Hawkens" sold by various makers before the inline craze started are really semi-copies of New England half-stocks. Many are good shooters, just not very authentic, if that matters to you.
