Breaking News....
I have found an answer.
If you have a 1978 engine I have confirmed that the 1969 - 1976 Intake and Exhaust valves are compatible with the 1978 CB750K SOHC Honda as follows:
- The 1978 OEM Valve Cotter part # 14781410000 must be replaced with 1969 - 1976 OEM Part # 14781551000
- The 1978 OEM Valve Spring Retainer part # 14771410010 must be replaced with 1969 - 1976 Part # 14771551020
- The 1978 OEM Intake and Exhaust Valve part # 147111300015 and 14721300015 must be replaced with 1969 - 1976 Part # 14711300005 and 14721300005
- Valve Stem Seals remain the same.
- Valve Springs (inner and outer) remain the same.