I think that shelling corn at the header is some sort of speed problem, not a stalk roll problem unless they are very worn.

As I recall from years ago, The concept of the header is to pull the stalks down within the length of the straight flutes on the rolls and the plates. This is then a relationship between the forward speed of the combine and the header/roll speed setting.

The only time stalks rolls themselves would enter into shelling is if they are so worn that they do not pull the stalks down. Replacing them with any new ones or resurfaceing/building up the old ones should take care of that.

The choice between various types of knife rolls or the standard JD cast iron is really one about the residue. This is really related to what and when is the next operation in that field.  If you are going to run some sort of shank type tillage machine thru that field in the fall, often folks want the cornhead to be aggresive in sizing the residue and separating the stalk from the rootball.

Without getting into a long discussion on the relative merits of different tillage systems, for a strip till system I like to leave the stalk attached to the ground so it stays put over the winter. I also like to leave residue standing rather than in a thick insulating mat on the ground. Standing stalks mostly attached to the rootball catch moisture over the winter and don't blow to the fenceline.  Standing stalks harvested with the head run as high as possible also push over rather than into tires if you drive over them in the spring. They also help reduce compaction and inprove traction in many siutuations when driving on the stalks. Short, tough stalks poke into tires rather than lean over and under tires.

To get back to your question, if your rolls are sop worn that you are not pulling the stalks down within the plate length you can replace them with ANY style new proper diameter roll or resurface the ones you have. There are several companies that do that and they work as good or better than new when they are done  (some resurfacers machine or grind them round after surfacing).

Best of luck.

Jim at Dawn