The famous French 75 was the Model of 1897, so breech loading, hydraulic recoil absorbtion, and many other features predate 1898. The primary concern of the ATF seems to be self-contained ammunition, that is, primer, charge and projectile as a single unit, as well as exploding projectiles. Stay away from them and you appear to be OK.
However, your state may have additional restrictions that you should check out.