I just looked at the blower on JD Parts, and I don't see anything showing that part as being part of a 54" blower. Maybe I missed it somewhere but I don't believe I did. Another member might be better at this blower stuff.
Hmmm....baffling. I also had a part I'm sure went where the two bearings hold the shaft. But I didn't see it on any others from YouTube videos so just left it off. I think it may have been an arrester in case a u-joint broke or something. Directions sure would have been nice!
So I got to thinking about the hall effect sensor for the snow blower that is used to disable the RIO when the front PTO shaft is spinning. Mine, which I didn't install, used a bracket mounted on one of the bearings to hold the sensor close to the PTO shaft and the wire connected directly to the harness on the tractor. In looking at a new 1025r (serial 1LV1025RLHJ100001 and up) in JD parts, I believe I may have found your mystery part.
It's part of the Front PTO Hitch (BLV10786) kit. Here is the drawing from JD Parts:
It looks like it's some type of bracket for the plugs for the hall effect sensor (instead of going straight from the sensor to the tractor wiring harness). I could not find any type of manual online. Perhaps you could snap some pictures of the bracket and parts you have left over.