very interesting puzzle! so, it's a BMW 700 prototype.
The final BMW 700 was designed by Michelotti for Denzel.
The front of this prototype can be found on the later BMW 1500.
So maybe this 700 prototype has been designed after 1961 as a successor for the BMW 700 as a smaller brother of the BMW 1500.
So it is not Michelotti? Maybe it's Bertone then?