Your
Krag action probably already has the 'guide lip' in place.
The rivet that anchors it in place is almost invisible, so the part seems integral with the receiver.
BTW - U.S. Krag Barrels were completely finished, ('clocked' threads & index marked, front-sight base brazed on, rear-sight holes drilled & tapped, proofed & marked, chamber completed, extractor-notch cut, and rust 'browned'/blued).
The Krag barrel never met its case hardened receiver, until the completely finished barrel was screwed on to the receiver and the index marks lined-up.
Krag barrels were basically made "interchangeable". 'Finish chamber-reaming', after barrel installation, and fitting the bolt were not required, like nowadays.