I'll be the heretic here.
I think its a restock of some sort. Buttstock has good architecture.
The rear of the triggerguard is more or less straight rather than having a curved finial similar to the front.
From what I see on lthe lock carving, it doesn't strike me as from tulle. Alot of the tulle guns I see have less curve on the forward end of the lock panel carving.
Two screws in the bottom of the buttplate is not a typical tulle feature also. Its common on fdc guns from st Etienne. I'd like to see the finial on the buttplate also. There are distinct differences on buttplates made at tull and SE.
The lock looks very representative of the ones from tulle.
Three forward ramrod pipes is not a typical feature of tulle fdc's.
No mention of any markings on the barrel. Whether on top or underneath,it would have been marked. No mention of caliber, length of the octagon section,or the type of transition to round. once again, there are differences
The front sight is in the right location for a French barrel . Typically you see them about four inches from the muzzle , placed over the forward pipe. Which was done also.
Without the gun in hand, or more detailed pictures of the buttplate or barrel markings. Its still hard to say.
Myself,I'd wager a period colonial French restock.
Thats what I gather from these photos.