The chains were like a wheel net used to quickly secure the skis on the front wheels. When removed there was a storage area under the bed of the GAZ-60 to store the skis.
Here is a later version of the GAZ-60 that was based on the GAZ-MM (note the lack of front doors - only a roll down canvas tarp) with a simpler track mechanism, which could be easily removed if needed....and again the chain wheel nets over the front wheels to secure the front skis: