I'm no expert on the Fusil de Chase nor do I claim to be, But, I've owned five accurate representations of the French Fusil de Chase and not one of them is exactly the same as the other, of those, two were custom built for me by two well known makers, two were custom ordered Center Mark Fusils, one in walnut and one stocked in maple, another custom was purchased by me at a local M/L shop.
The not so accurate Fusil was also a Center Mark that I purchased unfired from the original owner, I say it wasn't completely accurate because it was made with the lock on the left side of the stock, other than that IMHO it was accurate.
Now I've read many of the claims made by armchair experts and know it alls, trigger guards, lock plates, butt plate finals, entry pipes, and finally wrong barrel lengths, it's all so much BS.
Every maker of custom M/L arms has usually a library full of books, plans, and drawings as well as the history of the guns that they build and usually clear pictures of original guns, the bottom line being that they do their research to insure as much accuracy as possible.
I've also owned original guns of the late 17th and 18 Century including second and third model Brown Bess muskets, and one thing that I have learned is that no two guns are exactly alike, similar yes, exactly no, Guns in the 16th, 17th, and 18th. Century were built one at a time mostly by cottage industry, there was no tooling mechanized or other to hold tolerances let alone interchangeable parts.
Generally they were all different, there are examples of original French Fusils de Chase that have barrel lengths from 39" to 42"'s and even longer, stock dimensions are all different, metal furniture like trigger guards, and butt plates are similar but not exact.
Trust me, if you find two guns that are exactly alike, they were made by machine, and they are not historically accurate.
I still own and shoot two fine and historically accurate French Fusil de Chase smoothbores, both are made by Center Mark, one in walnut, one in dark curly maple, and being true to historical correctness, they are not exactly alike.