Please excuse my ignorance here, I have accidentally become a CB750 enthusiast only recently. I have what appears to be a K3 model with a manufacture date of 11/72 ( vin number 2213926 ) on the frame. The engine is also a K3 ( at least according to the book ) but it is different from the number on the frame ( engine shows 2216984 ) . Did this happen at the factory, or is this just an old engine swap? This thing is a crusty barn find that hasn’t been on the road since the eighties ( 12,000 mls showing on the odo ) . Also, would this be considered an early K4 or just a late K3? Thanks for putting up with such silliness, and I am sorry if this is not the correct thread for this type of question.