The bushings are not interchangeable. The new bushings must be oversize and finished in place because the holes for the bushings and firing pins were not bored perpendicular to the breech face. Making them requires that the new bushing be made longer than necessary, then screwed in place and marked for the correct orientation of the screw slot and correct length, then removed, the length trimmed roughly, the screw slot milled, then screwed back in for final finishing. Not a job for most amateurs.