Went to fit a used 45-70 barrel today - put it on and it locked right up. Smoked the shelf and the engagement was perfect. No work required.
At this point I have fitted 5 barrels on to two frames with nothing more than a very minor amount of shelf honing required. Not only that, the two frames are so close that the barrels interchange with no problem.
Needless to say, I couldn't be happier!