I see you say the cases have to be split on the DOHC engines on the other threads for this issue
http://www.cb750.com/threads/3800-1980-CB750K-Drive-Sprocket-Oil-Seal-Replacement
http://www.cb750.com/threads/4150-Countershaft-seal-split-the-case?highlight=Countershaft
The part number for the...