"35 W.C.F."
.35 Winchester Center Fire.  Typically a sign that a gun has been rechambered.  The marking is to let you know that.  Given that a Krag would have been made in .30, and it's now .35, it'd be logical to assume a barrel change. Get a .35 and see if the bullet fits in the end of the barrel. 

I'd think a Krag chambered in .35, without a barrel change, would be an interesting thing to shoot.  With a string from 300 yards away.

The first thing to do is check that bore size.

Wooops - more going on here than meets the eye!!!!!!!!!!!!

First off, there is no such thing as "off-the-shelf .35 shells". They (.35 WCF) are valuable collectors items, and may well have suffered powder deterioration and/or split necks. If you wish to shoot it you will have to load your own, using .30-40 brass and new .358 bullets.

The chamber may or may not be to SAAMI standards, but with a rimmed case that is not a great problem - and the cases will fire-form in any event. Using a heavier bullet means decreasing the powder charge from suggested .30-40 loadings. Work your loads up carefully - the Krag is not the strongest action around. Just as the .30-40 will almost match the .308 Win, the .35WCF will almost match the .358 Win.

You may have feeding issues - the Krag magazine was designed for ONE shape only. Since the gun is already altered, it may have had the feed surfaces tweaked as well. If not, no harm in doing so, since the originality is lost anyhow. The .35 WCF conversion, as well as various .35 "wildcats", was marginally popular in the 20's-40's for those who wanted heavier bullets, at the expense of some velocity.