Curious as to the extent of the Mods to the extra bbl. If you have to remove much from the "Face" of them then a recut of the rim seat may be in order. If you are referring to removing metal from around the perimeter of the standing breech because these bbls overhang then you could run into problems with firing pin strike, for if the bbls are larger, they also likely have a wider firing pin spacing. There is a lot to consider here before you go to "Cutting Iron".

Miller/TN
I Didn't Say Everything I Said, Yogi Berra