the true Ithaca and the Navy Arms Ithaca were not the same .
the original Ithaca was a fairly nice piece as was the Remington
I don’t recall Ithaca making a flintlock or navy Arms in their version .
I also don’t recall the Ithaca being offered in a kit . Only a finished gun . Myself I believe the piece in question is something someone has re worked .
As to the screw in the side of the breech being some type of sight mount with a blind hole . Could be . However I would not say it would be any different then cutting a dove tail . The reason I say that is that the area of the breech plug is normally considerably thinner in wall thickness then is the bore barrel wall thickness .
This then raises the question , at least for me , who did it , was it done properly , was it drilled clear through to the plug , was it not ??? We don’t know , the seller doesn’t say . For that mater he doesn’t mention anything as to what it actually is .
So while it could be nothing , it also could be something . We just don’t know .
But IMO when we add in the very poor quality job done on the patch box . The abomination of the washer on the lock bolt . Not to mention what looks like cheep craft store brass pins holding the wedge pin echelons in place , it makes me wonder .
just to many things that should be so easly done better to then turn around and say that a blind hole was done right