Not sure what the tank is, but definitely is not original to the model/bike or any other Ducati. Makes me think of an Ossa, but not quite. Fenders are wonky too, at least cut up (rear trimmed off parallel with frame) and bobbed (front) if not swapped as well. Rear looks more like a modified original. Front fender may or may not be, but it's still cut up. Wrong gauge & mount up top, should have speedo in head light shell (either shell isnt cut for speedo or is mounted upside down to hide that big hole) so extra $$ if both correct big headlight shell and speedo isn't there, wrong shifter, ...... You'll need get a correct round tank with good chrome and petcocks, two correct fenders and much more. So not "all there" as an original bike, but still could be a fun bike.
No matter- does anybody recognize the tank?