I figured it was a standard/common unit for IH. Any idea of a model #? There weren't a lot of IH planters ever sold around here and I have never seen one anything like it before. My dad had a set of cole planters on an IH three point hitch cultivator with something similar but I think it used a big rolling coulter/wheel to run the fertilizer attachment.
I first assumed that the hopper brackets were exactly like the Cub/Super A. I haven't looked at them side by side but I believe the bearings, and the way the brackets are cast to hold the bearings on which the hex shaft turn are made different than on a Cub/Super A attachment.
I will probably end up offering the fert. attachment for sale and would like to know what I'm selling first!