This is a great build of a very old paper model ( probably from the 60's ).
I am not a tank expert, but I have seen the IS-3 tank in person ( see attached of a captured Egyptian tank where my brother and I are standing next to ).
The IS-3 had a very rounded turret with no real flats on it.
Most probably they did not properly design it on purpose because it is too difficult to build out of paper.
I know, I built an IS-3 tank years from Maly company, and completely re did the turret using plaster. I did not finish the model thou. Here it is as well
Isaac