Don,t laugh at the new turrets.I have just drawn one of Mrs Bombhead's saucepans.Looking at the scan of the turret arrangement close up you see there is not a lot you can do to make them more detailed,any ideas?
That is a fantastic photo of the Eagle, and look at that air wing!
As to how to draw the turret there are lots of good images here:
And links to the Vickers photo archive with images of the workings of the actual mounting.
One thing about these turrets is the exterior of the house is very simple so there really isn't much to draw unless they are pointing straight at you.