I don't know first-hand, but, FWIW:

Joe Poyer in his book, "The American Krag Rifle and Carbine", describes the front carbine swivel-screw (for the 'saddle-ring bar') as being .60 inches long and the rear-screw being .885 inches long.

Poyer says the rear ('saddle-ring bar') screw is the same as the butt-plate tang screw.

It appears the rear carbine 'saddle-ring bar' screw also has the same dimensions as the rifle 'butt sling-swivel' screw(s).

A pair of Krag (rifle) 'butt-swivel' screws, with one shortened to .60", should do the trick.

Grandpa's Gun Parts (in KCA Classifieds) has these screws on sale for $3.00 each.