Many Dickert rifles were converted to percussion and that would be a good route to go. Another choice would be a Hawken style if you can find a wider butt plate. I got one from Tip Curtis which had the same curvature as a Hawhen but was a full 1 1/2 inch wide, not as sharp a crescent, and it's a comfortable rifle in .54 cal with full loads. A tapered barrel 1 1/8 to 1 inch would be appropriate, though the 42 inch length is longer than typical but not unheard of. with full loads in .58 cal, weight is your friend. I would want at least 10 to 11 pounds.