High Power, welcome to the KCA where you will get great feedback about your Krag carbine. I'm a 1911 collector and shooter from many years back and have been active in collecting, repairing, reloading for and shooting Krags primarily for the past few years. I have learned most of what I know about Krags from this website and its great members and reading through many of the recommended references about Krags like Poyer , Farmer and Mallory (and a host of others).

It does indeed look like you have wandered into a great find! The 1898 Krag carbine is one of the more elusive and mis-identified of the Krag firearms out there. The serial number range needs to be correct, the barrel needs to be of correct length, the patina needs to roughly match and the rear sight is best to be a carbine marked sight.

You have most of the above and especially, which you didn't mention, you appear to have an original early saddle ring stock that was used by the calvary to carry the carbine. It is difficult to find an early 1898 carbine sight and many of these carbines can correctly have the 1901 carbine sight on them. A lot of them had the 1896 carbine sight affixed to them at the arsenal. These are hard to find and can cost upwards of $600 for a good one!. The sight you have put on yours is certainly OK until another is found. All of the Krag sights, rifle and carbines, have the same spacing for the two screws but, as you have discovered, the hand guards are different.

Your carbine stock looks to have been refinished at some time and the receiver looks like it may have been reblued also. These are not that important considering the rarity of your carbine. Only 5002 of these were made.

How is the bore? Is there a set of cleaning rods in the butt compartment along with an oiler?

I can't believe what you paid for this treasure! Great find. Keep looking for parts and you may find a perfect sight for this one.

Welcome again and more people will chime in about your carbine soon.