To answer your original question, the vent windows are all interchangeable, though the 55 may have the little chrome shield above the window, which the 56 doesn't . It is not a problem though because the shields can be swapped over just by drilling out rivets and replacing. All the frames are the same. Of course Victorias and Convertibles are different, though they are interchangeable between years also.
I have just gone through a set of vent windows for my 55. I thought it was interesting that the Ford manual states that you can change the glass without removing the frames from the car. Pretty obvious, though for us now, if the glass is shot the seals probably are too.