Hi Olivier
That Belgian M41 is interesting, it's a late version with single roof pintle but has early all steel idlers & squared fenders, normally seen on earlier M41.
Was the serial number displayed? - There is normally a plate inside the drivers compartment on the left hand wall, with the serial number on it, or failing that, stamped at the top of the modification plate on the rear plate beside the tank/infantry phone.
It also has the late pattern smooth Commanders cupola, versus the early version with buttress's between the vision blocks. I couldn't see a cast number on the cupola - typically they are either in front to the TC's sight or on the left hand side of the cupola, below the sight guard, vertically aligned - perhaps you noticed it somewhere else?
Mal