1867 navy carbine authentication help needed

[Ayorique]

Hello,

I recently purchased what appears to be an 1867 navy carbine, in the original 50-45.
It has the correct extractor, P FCW anchor on the right, anchor on the barrel, FCW cartouche on the buttstock (none on the forend), serial number 4880 on the barrel, possible replacement rear sight and 1866 two line patent info on the tang.

What has me questioning it is the “assembly” numbers on the upper and lower receiver.
It has 37478 on the lower and 37478 with an over stamped 5 under the 4 on the upper. I found a reference to this “assembly” number in an IMA page for a carbine they sold. But wonder if that is really correct for an original 1867 navy carbine.

Thanks for any help you can provide.
https://www.ima-usa.com/products/origin ... 9860915366