I have Frame #CB7501043488 with motor #CB750E-1043501. Production was June 1970. According to the HONDA ID book, the K1 model started with frame #1044650 and motor #1044806. That indicates that my bike was made about 1300 before the model change. The pipes were HM300s, the seat has a duck-tail, and the oil tank is the typical K0 requiring the squarish sidecovers.
The bike came to me with a few parts missing..........no tank, no front end parts except I did get the cut fender and the front wheel. The carbs on the bike were the cam-type with the double cables but no airbox. I have no original painted color parts.
The clutch cover has 10 cap-screws.
Apparently HONDA began to make some changes before they began the K1 production with the rounded oil tank and the corresponding changes to the sidecovers.