Sgt - I am not an expert in this area - but herre are a few places to check:
1- go to a site 5madfarmers.com he has a lot of good info posted on Kragicon Rear sights with good pictures.
2- There is a guy on the Krag Forum (Krag collector Assoc) who sells nice repro handguards - he has some good pics on the site of which Handguard goes with
which carbine. Here is URL - Krag (Springfield) Upper Handguards

You say you are getting a 20K serial number carbine- that is most likely NOT a 1899 Carbine - would be much earlier based on serial.