Hi,
The actual range of elevation of a Boulton Paul type turrent wasn't more than about 100 degrees. THe latter element of the feed was (IIRC) loose enough to alow that amount of motion. I have photos of the defiant turret (inc some interior ones) here:
Defiant Walkaround and a photo of the air min diagram. I'm trying to say it's less of a problem than you might think!
Cheers