After a bit of web sleuthing, I think the gearbox is actual a "GEMMER" unit. Try cleaning up the casting more thoroughly and I think you will at least confirm this to be the make. I have attached a sample pic from an overseas supplier below that has an exploded view of a generic GEMMER steering gear unit that seems to very closely look like yours.
If you do some web searching of your own, research "GEMMER" steering and you will find quite a few places with some history of the brand and even some ideas as to what vehicles they were originally installed on. This
HAMB thread on Gemmer steering boxes has some interesting info.
The best way to further confirm will be to remove the unit and do a thorough cleaning that will probably expose casting numbers elsewhere on the unit. Best of luck in pinning down the details!
