PAUL - About everything Canton made was steel. Like You said, it was the old P&O Plow Works IH bought. Friend I worked at FARMALL with and also drove O-t-R with worked at Canton in Production scheduling for many many years, His Dad was Captain of the Plant Guard, so like many families at all the IH plants, it was a Family affair.
They had "Steam Hammers" at Canton, which are normally used to make forgings, so very possibly they made forgings for plows & other equipment. They look like castings unless You know how to look for the parting lines from the tooling. When I was dealing with the Canton plant in '79 the steam hammers were hardly used anymore. By then IH's BIG forge shop was in LVL. The biggest foundry at that time was also LVL, any castings Canton would have needed would have come from there, unless the needed Ductile or Nodular iron, that would have come from Waukesha.
But Canton did do a LOT of heavy metal bending. They made the side rails for the FARMALL's, then eventually the 3-point draft arms, they cut & bent the entire front frame for the 2+2's, and eventually welded the whole assembly for FARMALL. They also made the cab steps & battery boxes for Farmall. Most of that work transferred to Canton from E.Moline. E.Moline was having a terrible time getting ANY parts for themselves or other IH plants. I guess the Axial Flow combine released in '78 was too successful!
When I was dealing with them several times a day they would ship two or three 45,000# truck loads of parts daily just to FARMALL alone, and probably that much to E.Moline & LVL.
My Buddy told Me that the Canton plant had a steel dock & storage yard outside of Canton on the ILL River. They'd get steel on barges from WIS. Steel. The yard covered 40 acres with enough steel You could walk the entire yard and never have to touch the ground, just walk from bundle-to-bundle on the steel.
Wife & I did a Sunday drive to Canton in early '79 when I was dealing with Canton all the time. Downtown Canton was kinda cute & homey, the little central city square park with the IH plant across the street to the south. Place mostly burned down years ago but they haven't torn the rest of it down last I heard. There was an article about it in RPM 4-5 yrs ago.
Back in about '82 or '83 I made a delivery to an IH parts depot in West Chicago. I don't know if that was also their distribution Center also or not. About all I remember it was BIG. But IH's BIG parts warehouse was in Broadview, IL, just off 17th Street. It's a strip mall now, right across the street from a machine shop I dealt with at my last employer.
IH also had their own printing shop in West Chicago to print operators manuals, service manuals, & parts books. I ordered those also, and was able to get "SAMPLE Copies" of other manuals "As Required" And to keep this on topic, some of them were Cub Cadet related! ;-)