The CB650 cylinder head is remarkably different from the 500/550 head. The ports and valves are huge! Not just a little bit larger but a lot larger. The combustion chambers are unfortunately full-hemi, but that appears to have been necessary to fit the larger valves. This would also mean the valve angles are changed from that of the 500/550 also. Note that the 650 pistons are domed to compensate for the hemi chamber. The head I'm using has been modified to accept the 500/550 cam cover to retain the earlier bike's period look.