He ask the same question over on SOHC forum and I answered it with a picture from the Honda CB750 Parts List published 04 1969.
It is obviously NOT A SANDCAST schematic no matter how Yamiya750 has it labeled.
I also reviewed all of CMSNL's part list, all countries, all year models, and that schematic did not show up.
Not sure where Yamiya750 got it from. But DEFINITELY NOT Sandcast as KP said.
It pictures a ribbed air box so it has to be K1 or later as KP said.
I should add, I have never seen those items or that schematic previously and had not noticed it on Yamiya750.