As I stated before... 1898 Carbines HAVE been faked, and some very convincingly.  It's possible that you have a carbine barrel installed on a rifle receiver.  Or it's possible that someone did a good job of reattaching the sight post, although you can usually tell.  My guess would be that someone replaced the rifle barrel and stock with a carbine barrel and stock.  Mr. Hosmer would be the real expert here... and you can take his advice to the bank!

Is the sight a Carbine sight?  Look at the picture page.  There are examples of every type of Krag sight.  1901 Rifle sights are definitely different, and fakes can be easy to spot.