There is a brief bit of wartime film on Pathe of a Mk4 HAC turret turning around that has one of these mounted. Significant is that the distortion of the trees behind it indicate that there was a sheet of perspex nounted to the frame. Obvious that the map board itself is not set int he frame.
We made our own copy (ryan dis) and it mounts to two pointy spikes welded to the turret top. They have a flattened area near the bottom to receive a turn screw to lock the frame down.
Jim
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