There is a mod about this, it changes the type VII specifications to a IX boat
the exterior and interior model is a VII boat .
i think that a good way to the first Ix mod is change the external model an use the VII interior. but it requires advanced skills in 3d modelling, have the correct tool and deal with granny files.
here is
http://www.subsim.com/radioroom/showthread.php?t=187530