The CB650 cylinder head is remarkably different from the 500/550 head. The ports and valves are huge! The intake valves grew some 4mm. The combustion chambers are unfortunately full-hemi (though, oddly, oval), 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. At just a little over 25 degrees, it would seem so. Note that the 650 pistons are domed to compensate for the hemi chamber. The 650 head I'm using has been modified to accept the 500/550 cam cover to retain the earlier bike's period look.