Gil Irp's "IHC Tools" and all the IHC Parts Lists I've seen show the U50, U51 and UA51 as IHC Grain Drill wrenches.
As a side note all the parts lists Ive's seen show the two opening wrench but almost all found are the three opening version. The two opening ones as shown in The Wrenching News auction picture (#1149) above are fairly rare.