Thats a normal 750 seat lock, how about a pic of what you have?
Ok. So here is a comparison between the 2 different seat locks that I have. I have only ever seen a seat lock with the cover.
Have a seat lock with a cover that came off a K2 and a K5. The seat lock without a cover came off a K2 parts bike recently.
None of the bikes had matching key numbers for seat, forks, or ignition. Unaware if any of the seat locks were original.