dasBlute & tubeblue, Thank you. Neither the Mrs. or I are certain about the object. She thought it was a rangefinder, but even in WWI, the rangefinders were optical (Barr & Stroud) - not unlike the coincidence focus of a rangefinder camera. The front has a bushed hole - the bushing either giving precision location or to provide a replaceable wear surface - which could only come from rotation. A threaded adjustment in back would give minute rotation - appropriate for a gun sight (windage for artillery).
Thank you, Eric. 'Flying totally blind with them - having done only one attempt before. Some subjects are much tougher to shoot due to size/scale. One project from wife's dad was a *working* 2cyl air motor - powered by blowing into a tube. The whole thing, including tiny wood base is about 2" tall.