Ditto with Jerry, I bought a top single combo set from Pat at Dawson Enterprises, and as Jerry said, check out Pat's Stock Lock, Leo III and Jerry and many many others love em and the one on mine make a Nitro 27 feel like a 28 ga.! 330-833 0014, good luck, incinerate em!
If you still have your old Krieghoff, you may want to consider getting just the barrels. I got a top single from Dawsons and the over/under from someone on this site. They fit my old Kreighoff Hardware and I'm please with the results. However, I had a PFS stock and was able to deal with the higher ribs.