Additional photos would be nice. B&T made a small number of BT96 k guns for special clients that were marked MP5k (I have one). Some were semi-auto only and some were full auto. But the B&Ts that I know about were made in the early 2000s, not in the 1970s.
There isn't by any chance a circle on the side of the pistol grip? If so, that would indicate that it is probably a Chinese clone made by Norinco (they made MP5 clones, but I don't know if they made MP5Ks as well).