Corn row spacing usually determines wheel spacing. If you dont have corn, go as wide as possible. I dont know anyone who has wheels in the narrow position unless they have a 4-30 corn head. Tom in MN
If your hammers are rounded just on one side, you can turn them over. There should be no worry about their balance. They should have all worn the same.
If you do need to replace, consider the sharpened beveled type manufactured by loewen. They chop the straw up so fine, that the straw falls to the ground instead of sitting on top of the stubble.
If you turn hammers,make sure you put them back in same slot.Do NOT take all hammers out and put in one pile,then reistall in chopper.If you replace hammers they come in sets of three. They are installed as so they are about opposite each other.