Actually, if you look at many of the London makers of the period, they did dish the breech plug face in many instances in order for the back of the pan to line up with the breech. American makers often tended to just shorten the breech plug, which would be more of a safety concern, as it should be, today. But most American rifles are all over the place with where the back of the lock pan hit, and it just didn't seem to be important to them. In the past, I try to position my liners like Mr. Sapergia demonstrates in his photos. It is not incorrect for American arms.
As Smylee Grouch mentioned though, the position of that front lock bolt is important. This is best to get perfect if at all possible... Right between the barrel inlet and ramrod hole. Get it slightly low, and you will have to index and modify your bolt. Slightly to high, and you will have to groove the bottom of the barrel. Either of these scenarios is not tragic, unless done to the extreme, but they can be dealt with. Also consider where you want those threads to exit the lock plate. Some find it aesthetically disturbing not to have the bolt centered in the lock plate. So you really have to be thinking about all of these things simultaneously when laying out where you want the lock to go. Good luck.
M. E. Pering
