951B Track Loader

I am looking into buying this 951B Track loader which is about 3hrs away. The seller sent me these pictures & is not sure where the serial # tags are located. Any idea where they are located on the machine on a machine of this vintage? On my D4D there is one on down below the instrument panel & one on the back of the machine. I just wanted to have him give me the serial # so I can check the age of the unit. Metalman