I can say with some certainty that the books showing the front gun only had a slew in the vertical of +&- of 25 deg is most likely wrong.
Taking another image of this white tailed KI-67 & cropping the nose cone down to the second image. I gave it to a squad mate who works with Cad Cam & asked what angle he found using the software.
His findings were -34 to -35 degrees.
One thing to keep in mind with the above image is that we don't know if that gun in the photo is at it's total slew downwards. It could possibly go downwards even more. If the turret can rotate 360 degrees with these findings it will also give us +34 to +35 degrees in the vertical.
Changing tact a little also found an image with a KI-67 with no nose gun in the cradle & you can see fairly well the wishbone fixture as I called it. After seeing this more complete view it's more like an X shaped bracket than a Y shaped one.
Colour coded it red like the other images of it.
It seems to be in a different location than those other images with the guns installed. That maybe why it is set so far back
not attached to the gun yet?