The most popular replacement chaffer for CASE IH machines has been the 1 1_8 spacing with the long tooth. For more capacity in corn some prefer the 1 5_8. We also have the new GATEWAY plastic units that are lighter weight and easier on bearings and hangers.
We put a peterson non adjustable in our 1460 and loved it. Had an adjustable on in our 1680 and did not like it because it kept filling up with cobs in corn no matter where we set it. The 1680 was the only combine we had with a chopper in it so that may have been the problem.
Do you remember the cost of the air jetIJ There is a place on this site where you can request info on Gordon parts but I have e-mailed several times with no response.