Don't be afraid of an IH. Knives on IH can be turned front to back to be used again. There should be 1_32(IJ) of an inch tolerance as they pass each other. I have about 5000 acres on my head and they have been turned but never replaced. Check to see if tension springs on gathering chains have been drawn down to the stops. This would be a pretty good indication of how much life is left in gath. chains. look over bearings and chains around coupler to combine. Also pick up head to see what slip cluthes on row units look like.