Can you remove the parts from one to build up the other?

The part you have that is broken does not adjust windage.  It locks the slide that controls elevation by its position on the radius of the sight base.  You can remove the sight leaf from the base by driving out the pivot pin (left to right) with a brass punch.  Maintain pressure on the leaf and its spring before fully removing the pivot pin.  When the leaf is free from its base, the slide can be moved forward off the leaf (be careful because there is a little spring and pin that fall free, as the slide is removed from the leaf).  There are many variations in Krag sight parts.  Joe Poyer's Book - "The American Krag Rifle and Carbine" is available from sellers on the internet, usually for under $20.  This Work does a fine job explaining the various sights, changes, and variations.  Lots of minor sight parts for the Krag are available from S&S Firearms, Glendale, N.Y.  Their catalog can be viewed on the internet.

Both sights are model 1898 altered to 1902 format.  If one of the rifles has an 1903 cartouche the sight is a replacement.  Given the 1898 altered to 1902 was an analog of the 1902, as made, sight the replacement is "model" correct as a replacement but not for as made.

The slide up peep was added when that sight was altered to 1902 format as all 1898 sights were made sans that peep.  The other sight simply didn't receive that mod.

Cheaper to buy a sight than fix that.  On a good day a loose sight can be had for $26.  On a bad day they go higher. 

Thanks Very helpful.

Craig