The barrels simply dropped into place with no adjustments whatsoever, bolting tight to the breech face and with the opening lever correctly resting right of center. With a Smith Type II ejector gun the auto-ejector mechanism is housed entirely within the fore arm, so no frame modifications would be required. Assuming the existing ejector iron can't be modified to hold the piece that raises the manual extractor rod, you will need to find the appropriate R or FW extractor iron; and obviously find and fit an extractor rod/lifter unit in the existing barrels. A 12-bore iron can be filed down to correctly fit the contour of your frame if needed; and any grade iron could be used but would need to be engraved to be appropriate if not a Grade 2. Also to look appropriate, a Grade 2 manual extractor fore arm wood would need to be fitted with the round dogs head insert, ebony fore end tip inlay, and checkered to Grade 2 standard. As to fitting the replacement iron to the barrels, the replacement fore iron may simply snap into place; but most don't, and mine didn't either but was a simple fix. The problem is usually with the "J" spring being just a tad too long, as was true in my case; so I slowly and carefully filled and tested until my iron fit correctly. Again, I'm not a gunsmith but hope this helps some.