Both Frankenstein and the "Serious" 870 I use for deer hunting were switched over from 2 3/4", "V" models. IIRC, changing barrels and the ejector did the trick. I recall the smith telling me at the time that if there were feeding and ejection probs to bring them back to have the port enlarged, but never needed to....
However, the only real reason for switching over at that time was to handle big specialty rounds for turkey and waterfowl. This, due to the improved performance of non toxic pellets other than steel, is not nearly as important now.
Considering how many critters I killed cleanly with the older lead loads in 2 3/4" hulls and how the expensive but even more effective Hevi Shot outperforms steel by a huge margin, I'd be tempted to leave an old campaigner be and upgrade the ammo instead.
If I just HAD to change for the sake of change, I'd get the cone taper recut and polished to about 1 3/4". While the reduction in recoil may not be noticeable, the improvement in patterns will.
HTH....
