MIck seat is most definetely not off a CB500K, there are or seem to be 2 seat pans in the pics, neither are even remotely close to being off a 500. The first pic I have no idea what it is, the second is probably off a CB360 as it seems to be stamped with 369 and that's the CB360 model code.
Here's my NOS CB500K1 seat just before I sold it, look at the layout of the rubbers, the placement of the handbook pouch and the place where the hinge bar would go, not there on that pic but you can see the 2 bolts it goes onto.
This is a CB500K2 seat, same layout, only the seat cover pattern changed.
If I had a CB500K0 seat it would be identical except that never got the handbook pouch and the seat lock plunger was much different as it used a different locking system.