I see you've got an early Humphreys sight there, left drawer back center: https://www.milsurps.com/attachment....0&d=1400495572

I found the arm of a better and later version recently. There are no patent records in Canadaicon I could find though, despite the patent claim on the sight.

If anyone has a base I would appreciate seeing a few photos. I think Lyman may have inspired the toothed arm. (Sorry about the bad photos)