I have an original trapdoor carbine with a Buffington rear sight. While I find the Buffington a fine sight for shooting from a bench, for quick target acquisition shooting at 50-75 yards I find I would prefer one of the earlier trapdoor carbine sights. Before I order one, my question is: are all the various trapdoor rear sights drop-in interchangable? I certainly don't want to go drilling on an original trapdoor barrel.