As you already know the K-2A is a ball socket mount for the .30 cal ANM2 flex gun. This is the same mount used in all sorts of WWII aircraft including the early B-25's & B-17's, B-34's etc. Here is some information that might be helpful to you.

I would think that the aircraft manufacturer's drawings might have outline and assembly drawings but likely will not have the production drawings for the mount as it was GFE. There is a chance I might have the prints on a set of microfilm I have but it will be spendy to get them scanned. I would ask Jay Wisler as I bet he might have one for sale or know where to get one. Carl Scholl may have one too.
Here is one in our collection:

It still has layers of Plexiglas between the mounting flanges.
The K-2 didn't have the spring loaded cap to keep the wind out like the K-2A. There were usually several of these mounts used with one gun that would be slipped into the socket in the direction of the attacking aircraft. In the early B-25 the gun was stowed on the right side of the nose and there was a K-2A mounted in the nose and left side of the bombardier's compartment. These sockets would mount directly in the plex sometimes without any additional support.
Here is a photo of a field mod where they put 6 50's through the glass nose. You can see where the K-2A socket was mounted originally in the nose and the left side and has since been blanked off.

The K-2 and K-2A were cast and the K-3 was stamped. The K-4 was similar but for the ANM2 50 cal gun.
I hope this is helpful,
Taigh
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Taigh Ramey
Vintage Aircraft, Stockton, California
http://www.twinbeech.com'KEEP ‘EM FLYING…FOR HISTORY!'