well, that is one very important detail on which to distinguish the ships and their weapons, so I suppose you should add them! also, IIRC, there should be things sticking out the sides of the back of at least some of the turrets, which were part of the fire control system or at least were used to aim the guns. things like these are exactly what you should take from pictures, so keep up the good work
EDIT: also, I think those bumbs are because the diameter of the barbette is in this case larger then the width of the turrets.
and last but not least, tone down the width of the 'rounded' shading on the barbettes a bit, they look octangular now....