Some more info:
It seems there were 3 different aft designs regarding propulsion,but i can only find pictures on 2 types,so we must assume this was the standard type mostly build..
The more i look at real pictures the more i see its compactness,its not as stretched as you might think,they look very sleek in the water,therefore your model isnt that bad,it needs some more smoothing and an interior,and there is another problem,the launching of torpedos and mission!
I found this site with alot of good pictures:
http://www.one35th.com/seehund/sh_museum.htm