Stan,
Without a few photos all I can do is guess. The last date on the tang is "1866". The crown on the side of the receiver indicates that it MAY be from a Spanish contract. However, your bore description sounds too large for the .43 Spanish generally (altho I have a couple with groove diameters of approx. .448"). Your barrel length is definitely non-standard. The usual length for Remington carbine barrels is 20-22". The only Rolling Block carbines that I am aware of that had a hole thru the front sight were made by Nagant in Belgium for the Dutch. The hole was used to affix either a sight protector or bayonet. Your rear sight is graduated for a full length rifle (32-36" barrel). So, my guess is that you have a rifle that has had its barrel shortened at some point in time. With the Remington markings on the tang I can not explain the hole thru the front sight. The piece behind the trigger guard sounds like the rear sling swivel bracket with the loop removed, further indicating a cut down rifle.
Tom