The central part of this mounting that pivots vertically (roughly wedge-shaped plus the barrel) looks rather like the drawings of Zenith and Marquardt versions of DACR at 34 or 40mm. These usually show things like calculated recoil forces, but it is never clear on those I have seen how the gun would be mounted on a ship. This might be the answer. The whole turret is not unlike the 57mm twin DACR. Still can't get at my photos though.