Different layout of the engine deck.
The Tamiya kit many years ago had the Soviet engine deck BUT they inlcuded markings for two Polish tanks. There was also markings for a Czech tank.
The Polish markings were useless, at least for those who knew too much, since the kit did not contain the Polish engine deck.
The Czech engine deck is different from both the Polish and the Soviet one so those markings were "useless" too.
The Czech and the Soviet versions have the same mantlet but the Polish one is different.
lots more here:
https://armorama.kitmaker.net/forums/167910&page=1 / Robin