The Armstrong Whitworth turret (the birdcage type) was an extremely simple, non-powered, defensive turret for the Anson in its original G.R. role. I doubt it would have been of much use in training Air Gunners destined for powered turrets.

I think the turret you are referring to would be the Bristol (Blenheim) type. This was also fitted to Fairey Battles converted for training use.

Here’s a pic found on t’net.