Howdy!  Welcome to the forum, and to the wonderful world of Krags.  Careful... they're very addicting!

You can raise that elevation slide up to remove the bolt.  The Redfield sight should have a screw on the slide that you can set to hold your elevation setting, so after you re-install the bolt, you'll lower the elevation to where you had it set without changing anything.

Serial number is a model 1898 rifle.  If the barrel is not 30 inches from muzzle to closed bolt face, then it has been cut down, which is common for sporters.  Pictures will provide a wealth of information and you'll get great advice!