Welcome, Jason

I don't think I have ever seen a recoil pad fitted like that before, but maybe if (big IF) the stock has not been shortened, a new butt plate would screw right in place.

Finding an aperture for your Redfield receiver sight should not be a problem.  Most apertures for Redfield, Lyman & Marble, and maybe other makers, are interchangeable.  This should be a less than $10 deal at any gun show. Make sure that the bolt will operate with the replacement aperture in place.  Some apertures have large diameter sight discs that will contact the extractor when the bolt is opened.

Was your Grandpa a woods hunter?  He may have removed the aperture to let in more light.

Some receiver sights for the Krag required the receiver to be drilled & tapped to mount the sight.  Other receiver sights just fastened into the place for the magazine cutoff.  If the receiver has been drilled, the rifle is not technically restorable.  If the receiver sight is fastened via the magazine cutoff, you need to replace the magazine cutoff as a part of the restoration.

I will let someone else tell you about the missing rear sight and the hand guard and 1899 carbines in general.  Someone will advise you to buy Joe Poyer's book, which you should do.  It's the best $20 you can spend on your Krag.

The screw holes for the original rear sight appear to be on the barrel, so it is just a matter of $$ and screwing the replacement sight in place.

Unless the stock has been cut to add the recoil pad or the Redfield sight, and unless the receiver has been drilled & tapped to add the Redfield sight, I think your Krag can be restored. 

But if you did a restoration, it would sort of no longer be your Grandpa's Krag.  It would just be another restored 1899 carbine.