Aftermarket turrets

That sounds like a good "home" vacuform (heat the clear sheet over a candle and stretch it over the part) project using the originals as molds.

If I remember right, Koster Aero Enterprises makes a B-24J/PB4Y conversion kit
that has a sperry ball turret. It's the same turret that was used on the B-17.
Ray

Hey, Lucien! I know this isn't exactly what you're looking for, but it might get you on the right path...

I don't know if anyone makes aftermarket kits of just the turrets in 1/72 but i think swanny converted a B-24 (or was it a PB4Y?) into one with a ballturret in the nose position (I think). you might shoot him an e-mail to ask. Also, one of the first questions i asked in this forum is if anyone made aftermarket parts for 1/72 50 Cal guns... here's what i the guys/girls here gave me:
http://www.kitreview.com/reviews/karayabarrelsreviewbg_1.htm
Shame they don't make it in 1/72... yet.

Hope this helped!