Nah! Just have a look at how it works, copy the basic idea, and custom make one from timber and adjustable bolts/wingnuts etc, to hold any shape/scale you want!
Anyway, that rear turret. No need to make a fake frame - the rear, and bottom sides, were metal. Here's a pic of the B24 at Duxford. If you need any more detail shots, of this bird or others, just shout.