I've never seen that rib add-on, but the concept of an adjustable bead was out there. This is a "Bev-L-Block" sight (possibly with the bead broken off) which is shown on p. 210 of Brophy's "Plans and Specifications"
Raise the front bead = lower the POI
Raise the rear of the rib = raise your head = raise the POI
And the (purposeless) 'Celebrated Aubrey Disappearing Rear Sight'
http://www.meridenfirearms.com/patent.html
