I don't think that Ohio Steel Plows are all that rare. It's just that in the absence of any identifying marks like a decal, most people just automatically call them Brinly.
Ohio Steel made a lot of the same attachments as Brinly, and it's hard to tell the difference between the two.
Here's a link to a post that shows a number of Ohio Steel attachments that could easily be confused for Brinly attachments.http://gardentractor...__fromsearch__1
One way (I think) to tell the difference would be if there is any of the original paint left, as it appears that Ohio Steel painted all of their attachments red. But, like Brinly, Ohio Steel's attachments were also marketed under other Mfg. labels as well, and may have been painted to that Mfg's specs.
Here are a couple of pics of my Ohio Steel sleeve hitch for the Bolens tube frames.