I recently acquired a 1898 krag carbine, partially sporterized.  Good news is that it still has its original front sight, and no extra holes were drilled anywhere- with the original rear sight holes intact and apparently in good condition. 
I am hoping someone could tell me what rear sight belongs on this rifle?
Serial # is 292xxx (sorry Im at work and dont remember the last three numbers)
So from a little internet research it appears to be a 1898 carbine made in 1901. 
Any help would be appreciated.

I don't think it will be a real M1898 Carbine with a serial number that high. Most sources indicate that 98SRC serial numbers ended somewhere in the 130 - 140K range. They were all made in 1898 and the original sight would be a M1896 carbine sight. The stock would have the sling swivel/bar and would be the "short" version with a 1898 cartouche.

It does have a carbine barrel, so perhaps the barrel is not original to the receiver.  The stock has been replaced so I have no cartouche.  Should there be any markings on the receiver to indicate if it was a carbine?

Sorry if im asking basic questions, but this is my first krag.  I know i should buy a book. Thanks though

No distinctive markings on the receiver other than the serial number range to separate a carbine receiver from a rifle receiver. There were a little over 5000 M98 carbines made. Most of them were converted to the M99 carbine configuration at the arsenal by changing the stock to a longer version w/o the sling bar/ring. The handguards and sights were also changed. M98 carbines in the original as-issued configuration are scarce if not rare.

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Some pictures if you are interested.

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Shift_master:  You have a nicely sporterized Krag.  As others have pointed out,  it is most likely you have a "rifle" action re-barreled with a carbine barrel.  At the time your's was made, carbines used 1899 marked actions.  Your 'peep' rear sight was manufactured by Leroy Rice company, Elyria, Ohio.  It appears your stock was made to dispense with the action side-plate (on the left side).  Unless you luck into a carbine stock, you are probably best off enjoying your Krag as it is.  The 1896, 1901, and 1902 carbine rear sights would all be correct for your carbine barrel.  But you pay a high premium for an available carbine sight.  Carbine stocks and hand-guards are hard to find and expensive.  I would recommend you look into having some type of barrel band put on your Krag to anchor the barrel to the forearm.  Because the trigger guard screws are so close together, Krag stocks tend to split behind the magazine door, unless a barrel band is used.

Here is a picture of a Leroy Rice add from the January 1950 copy of "The American Rifleman" magazine.

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That's a very nice-looking rifle. Many re-worked Krags come out looking MUCH worse. From the placement of the front sight - which looks to be just a tad too close to the muzzle, I believe the gunsmith cut the existing rifle (that number was never a carbine!) barrel and reinstalled the sight. I do agree about the barrel band, but otherwise would suggest that you enjoy it as is - trying to make it "original" would cost a fortune.

I agree about the sight.  I thought my sporterized was a true carbine until Dick pointed out that the front sight (although correct) was also not properly located in relation to the muzzle, and the brazing used to secure it is actually visible too (bad job).  My serial number was much too high for a true carbine also.  You have a very nice sporter there though!  I wish my sporter was nearly this nice (purchased that way).