Hello,
I am new here but it appears I found the right place.  I have a M1898 ser #135xxx and just finished reading Poyers book.  It currently has the 1901 sight and type 7(Poyer) handguard.  I have the 1896 second type sight and screws and was wondering if I should get the type 3 (Poyer) handguard and switch them out to make it more original. 
     I cannot locate any cartouche marks either, is that a major draw back for value? Thanks for your help!

Wes C:  A caution.  Although Poyer's book is a handy reference and shows many of the variations of Krag parts, there are errors and unfounded assumptions.  His nomenclature is peculiar and drives some advanced collectors wild.  I find his book enjoyable and useful but some call it "garbage".

Wes C:  I don't believe the US Army or National Guard cared about bayonet dates matching production date of rifle.  That's a collector quirk.  Your 1898 dated bayonet with the 'smooth' rivets should also have smooth grips and is correct.  Your 1898 dated bayonet with the 'raised' rivets should have machining marks on the wood grips and is also correct and probably arsenal rebuilt.  I believe the change to raised rivets was approved in 1899.

Mounted on wood.

The 'Green' is verdigis, a copper oxide, caused by chemical action of chemicals in the leather in contact with the brass fittings.  Try Q-tips dipped in Neatsfoot Oil to clean sewn loops in the leather sling.  Clean brass parts with rag dipped in Hoppe's #9.  Dis-assemble sling and clean & soften straps with Saddle Soap.  Finish by wiping sling with rag dampened with Neatsfoot Oil.

Glad to see you refurbishing the sling and presenting it on a wall plaque. If the crack at the wrist of the buttstock is all the way through as it appears then hanging on the wall is the safest place for the weapon, at least until the stock is attended too.