I was involved with "the tail end" of a reconversion back to flintlock on an original Waters and Johnson Pistol, circa 1836, about a decade ago. The pistol's owner had passed before he had gotten it completely done and his widow wanted it finished as a memorial to him. I normally will not touch that kind of work, but my friend who brought it to me was a traveling man as had been the original owner. The pistol came to me disassembled in a shoe box with the parts in many plastic baggies.
The barrel, lockplate, and pan had already been reconverted. The cock and frizzen were original Waters and Johnson flintlock parts that matched the finish well, but not perfectly. It was a "scary nice" job done, but you could tell from the inside of the lock that the work had been done by the discoloration of the lock and a couple weld pin holes, plus the barrel condition where the percussion drum had been was slightly discernible.
Fortunately there were no side lock bolts with it and I decided to deliberately re-tap it and use modern side lock screws. I reshaped the heads on them a little different than original screws - so there were two more things that would stand out as a reconversion. The sear was broken, though I actually found two originals at a Civil War show and one worked great as found with a little work. The mainspring was broken in half, so I deliberately used one of Dixie's replacement mainsprings (instead of an original) so that too would be noticeable.
When the pistol was completed, I returned the broken original sear and mainspring in a small cloth bag that was to be kept with the pistol.
The widow was delighted and had the pistol framed in a glass covered shadow box for display and placed the cloth bag inside as I had requested. I wrote in pencil (because pencil lasts longer than pen ink) on two small pieces of folded linen paper that it was a re-conversion and date and tucked one under the lockplate and one in the barrel, but I told no one about them and they are still in the pistol. I also wrote a note detailing what I had done and the date, that I requested be attached to the back of the shadow box and the Widow did that as well. The Widow's son and daughter both want the gun when their Mother passes to keep the gun in the family, so for at least one more generation, it won't be sold on the market as a fake.
Gus