Have a look at:
www.dream-arts.de
Click on: on line shop at the left.
Once you are there click on Produktubersicht and then on U-boote turme.
The site is in German but you can easily navigate.
Here you will find images of the different variants of the type VII conning towers.
These images are excellent reference for the towers although that L shaped
duct you see on the B tower should be on the starboard side, according to my
references. Also there seems to be a ventilation duct which was attached to the
rear of the attack periscope housing, that is missing.
You can see a close up of this duct in a photo in the Squadron: U-boats in action.
Also have a look at photos of the Amati 1:72 U47 and compare.
Hope this can help,
Have a nice day and happy modelling,
Joe