Haven't done one myself but I hear lots of good about the Lyman Great Plains Rifle as to overall quality and authenticity. I built an underhammer
Hopkins and Allen kit recently. There isn't any inletting just shaping and finishing. The barrel was rough and requires smoothing and finishing. I did it with Thunder Mountain cold browning and it came out great. Those U-H's are great round ball shooters (1 in 66)and so elegantly simple. Nothing to break! Quick ignition! Accurate! Available many places in 36, 45, 50 cal.
A long time ago I built a TC Renegade and it's still my favorite. I shoot rould ball and bullets well and the wood is beautiful and getting better.