I built some tools and rebarreled a Krag recently. I documented some of it in this thread.   (You need to Login
If you have a milling machine the clamp for the receiver is not hard to build. Mine is 3/4 thick aluminum, with a 1/8 pin to place up next to the receiver box to prevent slipping. On mine it would not have been necessary as the barrel was not very tight. I placed the barrel clamp in mill vice with the vice jaws assisting the clamp screws and turned the action clamp with the Crescent "auto" wrench in the foto. Butlers Rangers said the Krag barrels are remarkably interchangeable, that to me suggests that some will be tighter than others to make the sights line up.
If you do not have a mill and can not make the clamp, send me a private message and I can lend you mine.