I've found only one web mention so far. A visit by a Spanish enthusiast. Written in Spanish, unfortunately.
http://www.armas.es/narticulos-Museo...os/000257.html
To answer some of your questions;
The frame had finger bumps as an integral part. It is as if they had cast a completely new frame unit including finger grooves. Another unusual variation were two large leafs extending down from the grip to completely enclose the magazine bases, which could only be grasped from front and rear. I don't think the standard magazines displayed with th gun would work. The magazines this gun would accept would need to have the lugs on the base flush with the magazine tube.
A sight base appeared to be welded to the rear of the frame, with clearance for the last toggle link to reciprocate within this base. An elaborate adjustable sight was afixed on top of this. The front sight appeared adjustable for windage via a spring-loaded catch and rack, (rachet). No tools needed, simply press latch and slide sideways. There was a wide trigger shoe on display for this gun as well.