Russia / Soviet use very clear and simple naming schema for their vehicles and ZSU-39 is nothing what it should be for the vehicle.
The "ZSU" (Zenitnaya Samokhodnaya Ustanovka) is direct acronym from "anti-aircraft self-propelled mount".
The next numbers explains the bore diameter in millimeters what in ZSU-39 implifies it would fire 39mm diameter shells, while in game it fires only 35mm. The naming should in game then be "ZSU-35" by logic.
There is as well a third numbering what is used to inform how many barrels does it have. It is not informed if it has only single barrel, but in this game the unit name should be "ZSU-35-2".
ZSU-35-2 follows the Russian type of logical naming like ZSU-23-2, ZSU-23-4, ZSU-57-2 and so on.
So correct naming would be: ZSU-35-2 "Tigris" if wanted to stay on old naming schema instead modern one what is used like "2S6M" what is weapons combination platform by KBP, so in game it could be example "2S9M Tigris"
ZSU-35-2 would be faithful to old schema.