Wow!  I'll pay you $600 for the Krag!!!

The 1896 carbine rear sight alone has been going for $500-$600 lately.

I can't quite make out the serial number.

As others have stated "clear pictures of the muzzle and front sight" would help a lot.

According to Brophy's "The Krag Rifle", All Springfield-made PCRs were marked with the inspector's cartouche, J.F.C.   However, not all PCRs will have the cartouche because of being manufactured at Benicia, Rock Island Arsenals or modifications done in the PI by the U.S. Ordinance Manila Depot.  The cartouche looks good to me but their are individuals who will stamp things to make them appear authentic.

Mallory's "The Krag Rifle Story" indicates that the standard sight used was the Model 1901.  Another interesting note is that at least 39 Model 1898 carbines were converted to PCRs.
(three at Springfield and 36 at Rock Island).

The rear peep sight appears to be a Redfield Model 70 but I'm not a peep sight expert.

Even if your Krag is not the REAL DEAL... it would be a fun project to turn it into a PCR replica.  Regardless, it's Kool Krag that I wouldn't mind having!!!

OK, one last offer... How about $650 bucks?  ;)