Iranian IS-120. Image: FARS News
Another blog post covering it is here http://covertshores.blogspot.com/2010/06/north-korean-small-submarines-file.html
Here are the latest estimated views showing the internal layout as discerned from video and other evidence:
There have been many iterations of these sketches and the 3D model, but each has differed in minute detail that only the most enthusiastic observer might notice.
The original schematic/cutaway sketch was by the blogger Plane Man. We can now see that it was wrong in almost every detail, but correct in many ways too. It acted as the starting point of this project.
Although the original source is not clear (if you know please tell us so that we can give credit!), this South Korean sketch which we found during research turns out to be very good, although not exactly as per the IS-120 model:
Another RoK illustration (author/source unknown to this author) of the related but smaller P-4 class submarine was also useful:
An earlier model of the MS-29 was created by TLAM Strike using SubSim game modelling approach.
Compared to the IS-120 model/sketches, the above MS-29 model has a more rounded nose and lacks the toothed edge between the upper deck cladding and the pressure hull. This is not incorrect, rather it shows some of the observed differences between the IS-120 and the early-production MS-29. The model shows externally mounted torpedoes which conforms to some DPRK defector accounts. This arrangement is either altogether wrong or more likely mixes up various DPRK submarines - whichever, the account of the defector are otherwise credible and extremely enlightening. William Magoffin was among the researchers contributing to this effort and has modelled many North Korean submarines, creating excellent visualisations.
The main break however came from several videos of the internal arrangement of the Iranian IS-120 shown on Iranian news channels and available in poor resolution on Youtube: