IHC ALSO used AMC 401's but they RENAMED THEM 400 to differentiate between IHC's native 401. This caused all sorts of confusion, because a "bright mechanic" would look at that AMC and say "I know what THAT is, THAT is an AMC 401."
So the "bright mechanic" goes to the parts store and tells the parts store guy "I have an IHC with a 401, and I need x, y, z"
So the parts guy looks up junk for an INTERNATIONAL 401 and the "bright mechanic" has to come back when the parts don't fit!!