but to be correct this car has its own nickname known for all polish car fans: "Syrena Laminat"
and it wasn't exactly a prototype beacuse this was a new body made to be a replacement for old used body od Syrena 104, made of some kind of plastic
You could made one like this and change with your old body
I believe they made 4 or 5 of those bodys in FSO (where Syrena was originally produced) and few more by a private mechanics
So You can call it protoype or not but better name is Syrena Laminat