Great photos Randy, thanks for posting them.
The B-17 and the B-24 ball turrets were identical in fact they typically had stenciling and placards for both the B-17 and the B-24 on the same turret.
Here is a placard/decal that I find particularly interesting...
Gee I wonder how they figured this one out?!
A few of the differences were the model number stamping and of course the retracting cylinder for the B-24. There were a few other bolt on differences like the fire interrupter cams and some warning light switches.
The ball turret in your photo was from a B-24 because of the bolts visible for mounting the ring gear carrier which was special to the B-24. All you had to do was to remove the carrier and you could install it in the B-17.
Collings B-17 actually has the B-24 ring gear carrier for the B-24 mounted. I think when they first put it in they didn't realize that it didn't belong. As a result the ball turret rides several inches too high in their B-17; a problem I am working on to rectify.
Here is a rare shot of the ball turret in the Collings B-24 extended on the ground. The aircraft was jacked up and stabilized for the fuel tank replacement surgery which gave us a good opportunity to work on the turret retract mechanism.
Thanks again Randy,
Taigh