No markings on the barrel? What caliber is the gun? Does it have a "lever safety" on the bottom tang like a '73? Early Navy Arms Ubertis had that safety and a short carrier for .38 spcl. Then they notched the front of the carrier window in the frame to allow for 44-40 with the same short carrier. Seem to have heard that Navy Arms made a run of either Henries or '66's in .44 Rimfire once as well.
I offer this...it is only as conjecture as to the origin of your Model 1866 receiver
In 1979 when Navy Arms Co. founder, the late Val Forgett, came out with a limited-production of 1,000 rifles,
500 chambered in .44 Henry and 500 in .44-40 Win. These guns were Henry's built in Mr. Forgett's own facilities in Union City, N.J.,
After this run, Forgett sent his tooling to Italy where he would have production incresed.
Henry's have been made by Uberti every since , that is until 2011 when Anthony Imperato's Henry Repeating Arms introduced
the return of the American made H011
Below is the receiver of one Mr. Forgett's 1000. Perhaps it will help in the identification of yours.
(EDIT)
posted the wrong photos earlier DoH !
I can't quite tell If yours has the second screw just below the hammer
if it does, then there you go...