Regarding the J. J. Henry lock, I never fully understand why, when a converted flint rifle still has its original lock plate, owners want to replace it with another original lock. Even if a similar J. J. Henry original flint was found, it's plate would not be exactly the same size, and there's a high risk that the bolt holes wouldn't line up well with existing holes...thus forcing more alterations to the original rifle and/or alterations to a previously untouched original flint lock.
Changing the lock out, even with another original flint, moves the gun farther away from its original configuration, and probably causes more, even if minor, alterations to either/both the rifle and the new lock being mounted. By doing a correct reconversion of the original lock plate, there are no bolt hole alignment problems, no slight alterations to the stock to make the new lock fit, etc., and the gun has been allowed to keep more of its original parts. I know people do it, but it never makes good sense to me to stick a different lock, even a good quality original flint, into a flint gun that retains its original lock plate. It sure doesn't make the gun more "original," and most of the time an experienced eye can tell the "original flint" is a later addition to the rifle. Shelby Gallien