I'm no expert on the turrets, but I had a chance to fly in the Collings Foundation B-24 a couple of years ago. On account of volunteering to turn the props, I rode in the radio op seat for takeoff, which put me right in front of the turret. I'd be able to tell you an hours worth of experiences from an half hour flight- highly recommended, worth the money. here's the two shots I took.
I've got a couple each of the nose and tail and ventral turrets, plus the cockpit which has an "upgraded" IP.
Speaking of -24's a friend who's his friend tells me Lefty Gardner is failing. Great guy.